[Emerging Infectious Diseases]
[Volume 4 No. 3 / July - September 1998]
Special Issue
The July–September 1998 issue of the journal will contain presentations
from the International Conference on Emerging Infectious Diseases (Atlanta,
March 8-11, 1998). Highlighted articles are currently available in
electronic format.
* About the International Conference on Emerging Infectious Diseases,
S.A. Morse
The following summaries come from satellite partnership meetings
* Plague Diagnostic Workshop, M.C. Chu
* The U.S.–EU Conference on Extension of the Salm/Enter-net Surveillance
System for Human Salmonella and E. coli O157 Infections, A. Levitt
* ASM/CDC/NIH Training in Emerging and Reemerging Infectious Diseases,
K. Western
About Emerging Infectious Diseases
* Collaboration in the Fight Against Infectious Diseases, The Secretary
of Health and Human Services Donna Shalala
* Effective Global Response to Emerging Infectious Diseases, C. Broome
* Addressing Emerging Infectious Disease Threats—Accomplishments and
Plans, J. Hughes
* Global Surveillance of Communicable Diseases, D. Heymann and G. Rodier
* Emerging Infections: An Evolutionary Perspective, J. Lederberg
* Emerging Infectious Diseases: A Brief Biographical Heritage, P.
Drotman
* New and Reemerging Diseases: The Importance of Biomedical Research, A.
Fauci
* Health Policy Implications of Emerging Infections, K. Hein
New Agents and Disease Associations
* Detection and Identification of Previously Unrecognized Microbial
Pathogens, D. Relman
* The Emergence of Bovine Encephalopathy and Related Diseases, J.
Pattison
* Explaining the Unexplained in Clinical Infectious Diseases: Looking
Forward, B. Perkins and D. Relman
The Global Threat
* Malaria: A Reemerging Disease in Africa, T. Nchinda
* Vaccine-Preventable Diseases, A. Mawle
* Travelers' Health, M. Cetron, J. Keystone, D. Shlim, and R. Steffen
* Global Tuberculosis Challenges, K. Castro
* Blood Safety, M.E. Chamberland, J. Epstein, R.Y. Dodd, D. Persing,
R.G. Will, A. DeMaria, Jr., J.C. Emmanuel, B. Pierce, and R. Khabbaz
* Confronting Emerging Infections: Lessons from the Smallpox Eradication
Campaign, W. Foege
* The Guinea Worm Eradication Effort: Lessons for the Future, D. Hopkins
Populations at Risk
* Nosocomial Infection Update, R. Weinstein
* Opportunistic Infections in Immunodeficient Populations, J. Kaplan, G.
Roselle, and K. Sepkowitz
* Host Genes and Infectious Diseases, J. McNicholl
* Immigrant and Refugee Health, S. Cookson, R. Waldman, B. Gushulak, D.
MacPherson, F. Burkle, Jr., C. Paquet, E. Kliewer, and P. Walker
Zoonotic and Vector-borne Issues
* Emerging Zoonoses, F. Murphy
* Influenza: An Emerging Disease, R.G. Webster
* Resurgent Vector-Borne Diseases as a Global Health Problem, D. Gubler
* Global Climate Change and Infectious Diseases, R. Colwell, P. Epstein,
D. Gubler, M. Hall, P. Reiter, J. Shukla, W. Sprigg, E. Takafuji, and
J. Trtanj
* Emerging Zoonoses, J. Childs, R.E. Shope, D. Fish, F.X. Meslin, C. J.
Peters, K. Johnson, E. Debess, D. Dennis, and S. Jenkins
Emerging Foodborne Pathogens
* New Approaches to Surveillance and Control of Emerging Foodborne
Diseases, R. Tauxe
* FoodNet and Enter-net: Emerging Surveillance Programs for Foodborne
Diseases, S. Yang
* Enhancing State Epidemiology and Laboratory Capacity for Infectious
Diseases, D. Deppe
Communicating the Threat
* International Cooperation, J. LeDuc
* Public Health Surveillance and Information Technology, R. Pinner
* Innovative Information-Sharing Strategies, B. Kay, R.J. Timperi, S.S.
Morse, D. Forslund, J.J. McGowan, and T. O'Brien
* Getting the Handle off the Proverbial Pump: Communication Works, L.
Folkers, M.T. Cerqueira, R.E. Quick, J. Kanu, and G. Galea
* Communicating Infectious Disease Information to the Public, E. Abrutyn
* APEC Emerging Infections Network: Prospects for Comprehensive
Information Sharing on Emerging Infections within the Asia Pacific
Economic Cooperation, A.M. Kimball, C. Horwitch, P. O'Carroll, S.
Arjoso, C. Kunanusont, Y. Lin, C. Meyer, L. Schubert, and P. Dunham
Critical Issues for the Future
* Controversies in the Prevention and Control of Antimicrobial
Resistance, D. Bell
* Infectious Causes of Chronic Inflammatory Diseases and Cancer, G.
Cassell
* Bioterrorism as a Public Health Threat, D.A. Henderson
* Bioterrorism as a Public Health Threat, J. McDade and D. Franz
* Who Speaks for the Microbes? S. Falkow
* Emerging Diseases—What Now? G. Alleyne
Letters
* Outbreak of Suspected Clostridium butyricum Botulism in India, R.
Chaudhry, B. Dhawan, D. Kumar, R. Bhatia, J.C. Gandhi, R.K. Patel, and
B.C. Purohit
* Molecular Analysis of Salmonella paratyphi A From an Outbreak in New
Delhi, India, K. Thong, S. Nair, R. Chaudhry, P. Seth, A. Kapil, D.
Kumar, H. Kapoor, S. Puthucheary, and T. Pang
* Unrecognized Ebola Hemorrhagic Fever at Mosango Hospital during the
1995 Epidemic in Kikwit, Democratic Republic of the Congo, M. Bonnet,
P. Akamituna, and A. Mazaya
* Classification of Reactive Arthritides, D.R. Blumberg and V.S. Sloan
* Reply to Drs. Blumberg and Sloan, J. Lindsay
* Cost of Blood Screening, O. Chang
Book Review
* Emerging Infections, B. Mahy
News and Notes
* CDC To Release Updated Emerging Infectious Disease Plan
* First Congress of the European Society for Emerging Infections,
September 13-16, 1998, Budapest, Hungary
* Foodborne Illness: A Disease for All Seasons, October 27 and 28, 1998,
Newark, Delaware
* December 1998 International Conference on Antiretroviral Therapy
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About the International Conference on Emerging Infectious Diseases
Stephen A. Morse
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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More than 2,500 researchers, clinicians, laboratorians, veterinarians, and
other public health professionals from all 50 states and more than 70
countries convened in Atlanta on March 8-11, 1998, for the International
Conference on Emerging Infectious Diseases. The conference, organized by
the Centers for Disease Control and Prevention (CDC), the Council of State
and Territorial Epidemiologists, the American Society for Microbiology, and
the National Foundation for CDC along with 62 other cosponsors,(ft 1) provided a
forum for the exchange of ideas and possible solutions to the problems of
new and reemerging infectious diseases, including potential threats
presented by bioterrorism. Several agencies and organizations sponsored
satellite partnership meetings on March 8 and March 12.
More than 85 sessions (12 plenary sessions, 17 invited panels, 35 poster
sessions, and late-breaking abstracts) were presented on surveillance,
epidemiology, prevention, and control of emerging infectious diseases, as
well as emergency preparedness and response and reemerging or
drug-resistant infectious diseases. Topics included foodborne diseases,
infectious diseases transmitted by animals and insects, nosocomial
infections, infections in immunocompromised patients and persons outside
the health-care system, infectious causes of chronic disease, blood safety,
host genetics, vaccines, global climate change, and immigration and travel.
In delivering the keynote address, Nobel laureate Joshua Lederberg reviewed
the scientific basis for the emergence of infectious diseases. U.S. Health
and Human Services Secretary Donna Shalala and Assistant Secretary for
Health and Surgeon General David Satcher, along with representatives from
the World Health Organization, the Pan American Health Organization, and
the U.S. Agency for International Development, and representatives from
academia and industry addressed the national and international
ramifications of emerging infections. In closing the conference, James
Hughes, director, National Center for Infectious Diseases, CDC, stressed
the importance of building bridges and forging new partnerships to prevent
and control the emergence of infections into the next millennium.
In publishing the conference presentations and discussions in this journal,
the organizers hope to capture the energy expressed by all participants,
further disseminate new information on emerging infections, and stimulate
more research and other initiatives against this important public health
threat.
(ft 1)Alliance for the Prudent Use of Antibiotics, American Academy of
Pediatrics, American Association of Blood Banks, American Association of
Health Plans, American Cancer Society, American College of Preventive
Medicine, American Hospital Association, American Medical Association,
American Mosquito Control Association, American Public Health Association,
American Sexually Transmitted Diseases Association, American Society of
Clinical Pathologists, American Society of Tropical Medicine and Hygiene,
American Veterinary Medical Association, Association of American Veterinary
Medical Colleges, Association of Schools of Public Health, Association of
State and Territorial Directors of Health Promotion and Public Health
Education, Association of State and Territorial Health Officials,
Association of State and Territorial Public Health Laboratory Directors,
Association of Teachers of Preventive Medicine, Burroughs Wellcome Fund,
Emory University School of Medicine, Fogarty International Center, Food and
Drug Administration, Indian Health Service, Infectious Diseases Society of
America, International Life Sciences Institute, International Society for
Infectious Diseases, International Society of Travel Medicine,
International Union for Health Promotion and Education, International Union
of Microbiological Societies, Minority Health Professions Foundation,
Morehouse School of Medicine, National Aeronautics & Space Administration,
National Association of City and County Health Officials, National
Association of State Public Health Veterinarians, National Council for
International Health, National Foundation for Infectious Diseases, National
Hispanic Medical Association, National Institute of Allergy and Infectious
Diseases, National Medical Association, National Oceanographic &
Atmospheric Administration, Office of Science and Technology Policy, Pan
American Health Organization, Rollins School of Public Health of Emory
University, Society for Healthcare Epidemiology of America, Society for
Occupational and Environmental Health, Society for Public Health Education,
The Carter Center, The Henry J. Kaiser Family Foundation, The HMO Group,
The Robert Wood Johnson Foundation, The Rockefeller Foundation, The World
Bank, U.S. Agency for International Development, U.S. Department of
Agriculture, U.S. Department of Defense, U.S. Department of State, U.S.
Department of Justice (INS), U.S. Department of Veterans Affairs, U.S.
Environmental Protection Agency, World Health Organization.
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Plague Diagnostic Workshop(sup 1))
May C. Chu
Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
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The Plague Diagnostic Workshop, cosponsored by the Centers for Disease
Control and Prevention (CDC) and the World Health Organization (WHO), was
held on March 8 and 12, 1998. Participants represented major laboratories
involved in plague diagnostic test implementation and development, the WHO
Collaborating Centers for Plague Research and Reference (Almaty,
Kazakhstan; Stavropol, Russia; and Fort Collins, Colorado, USA), the WHO
Collaborating Center for Yersiniosis (Paris, France), WHO headquarters, and
the Pan American Health Organization. Other participants came from Brazil,
China, Indonesia, Kazakhstan, Madagascar, Myanmar, Peru, Russia, South
Africa, Taiwan, Tanzania, United Kingdom, United States, Venezuela, and
Vietnam. From the United States, state and local public health laboratory
specialists from California and New Mexico, Naval Medical Research Unit #2,
and private industry personnel also participated.
The goals of the workshop were to assess the laboratories' capabilities to
perform plague diagnostic tests worldwide; discuss test methods; develop a
program for molecular characterization of Yersinia pestis, with emphasis on
monitoring drug resistance strains; and initiate worldwide electronic links
between laboratories. During the first session, representatives reported on
their countries' plague activities and presented results on improved and
new tests for plague. During the second session, presenters discussed
molecular methods used in typing Y. pestis and electronic methods for
linking laboratories through the Internet. Participants also met during the
International Conference on Emerging Infectious Diseases to discuss issues
ranging from plague diagnostic criteria to adoption of new test methods.
Recommendations were made to broaden and refine the plague laboratory
diagnostic criteria. Three working groups were created to evaluate and
develop international standards of Y. pestis-specific F1 antigen, F1
antigen-sensitized sheep red blood cells, and specific bacteriophage stock.
A fourth working group was charged with evaluating new diagnostic tests.
Guidelines and recommendations were made for molecular typing of isolates
using plasmid and protein profiling, pulsed-field gel electrophoresis, and
ribotyping. The workshop participants also worked toward establishing an
electronic bulletin board and soliciting support for another workshop in 2
years to certify the results of the working groups.
(sup 1)Summary of Satellite Session
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The U.S.–EU Conference on Extension of the Salm/Enter-net Surveillance
System for Human Salmonella and Escherichia coli O157Infections(sup 1)
Alexandra Levitt
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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To help extend the European Union's (EU) Enter-net system for the
surveillance of Salmonella and Shiga toxin-producing Escherichia coli
(STEC)(sup 2) to other countries, a conference was held on March 12, 1998,
under the auspices of the U.S.–EU Task Force on Communicable Diseases. The
conference was cochaired by James LeDuc (Centers for Disease Control and
Prevention [CDC], United States) and Christopher Bartlett (Public Health
Laboratory Service [PHLS] Communicable Disease Surveillance Center [CDSC],
United Kingdom), who head the Task Force Working Group on Surveillance and
Response. Attendees from countries outside EU (South Africa, Hungary,
Canada, Japan, Poland, Australia, the Czech Republic, Latvia, and the
United States) were invited to describe their countries' procedures for
monitoring Salmonella and E. coli O157:H7.
Enter-net, which has superseded the EU's Salmonella surveillance system
(Salm-net), is an example of "globalization in action." The network
consists of the microbiologist in charge of the member nation's national
reference laboratory and the epidemiologist responsible for national
surveillance of foodborne diseases. A collaboration of epidemiologists and
microbiologists working at the technical level, the network is not a
regulatory organization. It includes participants from all 15 EU countries
plus Norway and Switzerland, with a combined population of 380 million.
Since 1994, Enter/Salm-net has detected 10 international outbreaks
resulting from contaminated food or water, including one that involved an
Israeli snack food contaminated with S. Agona and one due to S. Livingstone
infection in visitors to Tunisia. Enter-net's objectives are to extend
Salm-net monitoring to STEC, including E. coli O157:H7, as well as
drug-resistant strains of Salmonella.
Enter-net participants are working toward a common set of laboratory
protocols, including procedures for serotyping, phage typing, and toxin
typing. They report disease cases to the international Enter-net database
on a regular basis, through the Internet, by using standardized data
fields. Every year, the participants from each member country attend a
workshop to discuss technical issues and principles of collaboration.
Potential conflicts addressed at workshops include ownership of data;
confidentiality; outbreak control measures; and liability concerns (e.g.,
what happens when a food product is implicated by Enter-net as a vehicle of
disease transmission). At the next workshop, which will take place in
November 1998 in Denmark, Enter-net members will review protocols for
collaborative field investigations.
U.S. representatives described U.S. procedures for surveillance of
Salmonella and STEC, including procedures for antimicrobial resistance
monitoring. While Enter-net relies largely on phage typing to define E.
coli O157:H7 subtypes, pulsed-field gel electrophoresis (PFGE) is the
primary E. coli O157:H7 subtyping method in the United States. In 1996, CDC
initiated PulseNet, a national molecular subtyping network for tracking E.
coli O157:H7. PulseNet is being expanded to include Salmonella and other
foodborne pathogens. PulseNet currently includes 26 state and large city
health departments and laboratories from the U.S. Department of Agriculture
and the Food and Drug Administration. An electronic database at CDC will be
accessible to all participating PulseNet laboratories and will include DNA
patterns of foodborne pathogenic bacteria and epidemiologic information
associated with these isolates. Like Enter-net, PulseNet requires that all
reporting sites use harmonized laboratory methods and standardized
reporting specifications.
Each month, Enter-net's coordinator, based at the Communicable Disease
Surveillance Center, applies an automatic cluster-detection algorithm to
detect international outbreaks. To make the best use of the algorithm, each
country must supply Enter-net with retrospective data from at least 3
years. The United States has an analogous system, the Salmonella Outbreak
Detection Algorithm (SODA), which analyzes data reported through CDC's
Public Health Laboratory Information System (PHLIS). Some U.S. state health
departments are beginning to use SODA to perform their own analyses for
incident detection.
Over the past few months, Enter-net has begun to define the data that will
be collected on isolates of E. coli O157:H7; the data will be incorporated
in an international database similar to the one used for Salmonella. The
network has also begun a survey of methods in use for antimicrobial
resistance monitoring in its member countries.
Enter-net's goals for 1998 are to conduct an inventory of national
laboratory practices related to the diagnosis of STEC and to antimicrobial
resistance testing for STEC and Salmonella, perform a multicenter study in
participating reference laboratories on the detection of drug resistance,
upgrade the Enter-net database to include STEC and antimicrobial resistance
testing, agree on an outbreak investigation protocol, pilot weekly on-line
reporting, and hold a scientific workshop in Denmark in November 1998.
Formal invitations will be sent to non-EU countries that have expressed
interest in joining Enter-net. Pilot data exchanges will be initiated in
September 1998. If possible, new members will begin routine data exchange
by early October and will attend the November workshop in Denmark.
For additional information on Enter-net, contact Ian Fisher (e-mail:
ifisher@phls.co.uk), PHLS Communicable Disease Surveillance Centre, 61
Colindale Avenue, London NW9 5EQ, United Kingdom. For PulseNet, contact
Bala Swaminathan, National Center for Infectious Diseases, CDC, Mailstop
C07, 1600 Clifton Road, N.E., Atlanta, GA 30333, USA.
(sup 1)Summary presented at a satellite meeting, March 12, 1998.
(sup 2)Previously known as verotoxin-producing Escherichia coli (VTEC).
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ASM/CDC/NIH Training in Emerging and Reemerging Infectious Diseases
Karl Western
National Institutes of Health, Bethesda, Maryland, USA
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President Clinton's directive on emerging and reemerging infectious
diseases calls for the development of domestic and international training
programs in this new and expanding field. A training workshop, which
coincided with the International Conference on Emerging Infectious
Diseases, provided an opportunity to exchange information on current
training activities; discuss future plans in clinical, public health, and
research training; and, more importantly, generate discussion on unmet
needs and improvement of present activities.
NIH Academic Partnerships: Needs and Future Directions
This part of the training workshop was chaired by the National Institute of
Allergy and Infectious Diseases (NIAID) Deputy Director, John R. La
Montagne. Each participant was asked to address the following five
questions: 1) What is emerging infectious disease training? 2) What are its
most important priorities and needs? 3) What are your recommendations for
curriculum development? 4) What resources are needed to address training
and curriculum needs? and 5) How can the American Society for Microbiology
(ASM), Centers for Disease Control and Prevention (CDC), National
Institutes of Health (NIH), and partners in academia, government, industry,
and professional organizations promote and support the training?
Adel Mahmoud, Case Western Reserve University, spoke about the problem of
incorporating emerging infections training into medical school curricula.
He was followed by David Stephens, Emory University, who spoke on the
integration of emerging disease training into infectious disease training;
Mary E. Wilson, Harvard School of Medicine, who discussed continuing
medical education; Gail Cassell, Eli Lilly and Company, who brought in
perspectives from industry and academia; and Robert Webster, St. Jude
Children's Research Hospital, who recounted lessons learned from research
in Hong Kong during the recent avian influenza outbreak. After questions
and answers cochaired by John La Montagne and Joel Breman, Fogarty
International Center (FIC), D.A. Henderson, Johns Hopkins University,
summed up the discussions and extracted recommendations.
The workshop had the following conclusions. 1) A number of emerging
infectious disease training initiatives either under way or under
consideration at CDC, the Armed Forces, NIAID, and FIC are modest (given
the training needs) and, without exception, underfunded. 2) There is
considerable public, private, and Congressional interest in emerging
infections, particularly in food safety and vector-borne diseases. 3)
Recently, a new element, biological warfare and terrorism, has been added
to the equation. 4) Several CDC training initiatives directed at local and
state public health authorities are frustrated by lack of resources in the
public health trenches. 5) Army and Navy overseas laboratories represent an
underappreciated and underutilized resource for training of both U.S.
citizens and foreign nationals. 6) NIH training is limited to formal
training; it sets ceilings on research training slots and its domestic
mission. As a result, most NIH research training is carried out through
research awards. The expansion of the NIAID International Collaboration in
Infectious Disease Research Program (with increased emphasis on training
U.S. scientists) and the announcement of FIC international Actions for
Building Capacity are welcome but are still short of what is needed. 7)
Industries' contributions, such as Merck's Mectizan and SmithKline
Beecham's Albendazole Donation Programs, are welcome. In addition, Lilly's
decision, announced this week, to provide CDC with funds for international
participants in its training program is an innovative approach to promote
intersectorial cooperation. 8) The recent Hong Kong avian influenza
outbreak is a paradigm on how the research, clinical, public health, and
industrial communities can cooperate in an emergency situation and prevent
a recurrence of an influenza pandemic. Hong Kong may have been a very close
call; influenza is the only reemerging infectious disease for which a
contingency plan involving all these players exists and is operational.
The workshop recommended the following. 1) Current CDC, NIH, and Department
of Defense training programs should receive additional funding and be
expanded through increased U.S. government resources and through innovative
cooperative efforts with the private sector. 2) U.S. Agency for
International Development (USAID), World Health Organization (WHO), and
other international organizations should join forces with domestic agencies
to provide for training of foreign nationals. 3) Increased communication
and coordination between the clinical, public health, and research
communities are needed. The veterinary educational model, which looks at
populations rather than individual patients, might serve as a model for the
medical community. 4) An intersectorial emerging infectious diseases group
composed of U.S. members from government agencies (CDC, NIH) and state
health departments, universities, industry, schools of public health,
professional organizations (e.g., ASM, Infectious Disease Society of
America, American Society of Tropical Medicine and Hygiene, and
international organizations (USAID, WHO) should be organized to identify
training needs. 5) ASM and other professional organizations should work
with academic institutions to promote curriculum changes at the
professional student, clinical training, and research training levels to
increase awareness of and capacity to recognize and treat or prevent
emerging infections. 6) continuing medical education courses, audiovisual
programs, and interactive educational materials should be developed to
address these training needs and should provide opportunities for
cooperation with industry and the private sector. 7) Intersectorial efforts
should be undertaken to train personnel and support work plans for training
and research that will help anticipate and control emerging diseases other
than influenza.
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Collaboration in the Fight Against Infectious Diseases
Donna E. Shalala
U.S. Secretary of Health and Human Services
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Two hundred years ago, the U.S. Public Health Service, of which the Centers
for Disease Control and Prevention (CDC) is an essential part, began as a
humble maritime hospital in New York City. Its mission was simply to stop
infectious disease from coming in on ships and spreading across our
country. Today, as we celebrate the anniversary of the Public Health
Service, another historic event has occurred. One of the great detective
hunts of the 20th century came to an end. Scientists at the U.S. Department
of Defense confirmed that tissue from a woman's body buried near the Bering
Strait contains genetic material from the 1918 Spanish flu virus—the virus
that caused the worst pandemic the world has ever known. This discovery
will help us map the genetic structure of the microbe that sent a wave of
death crashing around the globe 80 years ago.
It is hard to believe today that flu could be so nearly apocalyptic. In
just 11 months, at least 24 million people died, and most of humanity was
infected. The infected often never knew what hit them; in the morning they
felt fine; by night they could be dead—drowned as the lungs filled with
fluid. There was no explanation, no protection, no cure. The pandemic
produced scenes from a gothic horror novel—but it was all too real. In
Philadelphia alone, 11,000 died of the flu in a single month. The dead were
left in gutters, and death carts roamed the city in a surreal scene from
medieval times. As the deaths mounted all over the world, orderly life
began to break down. Schools and churches closed; farms and factories shut
down; homeless children wandered the streets; their parents vanished. The
acting U.S. Army Surgeon General, Victor Vaughn, calculated that if the
pandemic continued its mathematical rate of acceleration, it soon could
spell the end of humankind.
But then, as silently, as mysteriously, as quickly as it came, the terror
began to fade away. People stopped dying. The victims were buried. Life
returned to normal. The great flu was soon pushed off the front pages and
out of the public eye. When avian flu first appeared last year, we wondered
if perhaps another pandemic had begun. An influenza subtype that had never
before produced illnesses or deaths in humans now did. While it appears
that the spread of avian flu has halted without the appearance of
human-to-human transmission, the danger is far from over because the
critical period may be just beginning—this is the start of the traditional
flu season in Hong Kong.
The emergence of avian flu points up a broader concern: complacency over
infectious disease. It is easy to assume that modern medicine has defeated
this enemy once and for all. Our comfort is a natural byproduct of our
progress and success—the remarkable breakthroughs in antibiotics and
vaccines, thanks to the work of scientists and researchers worldwide. We
eradicated smallpox—consigning one of history's deadliest killers from the
medical books to the history books. But infectious disease remains the
leading cause of death worldwide and the third leading cause in the United
States. While we may be winning some old battles, we are struggling with
some new adversaries—emerging infectious diseases such as Ebola, hantavirus
infection, new strains of tuberculosis (TB), AIDS, and Lassa fever, to name
a few. In fact, the World Health Organization (WHO) has labeled the growing
threat of infectious disease a global crisis.
The time has come to replace complacency with a new sense of urgency—to
launch a renewed, unified, global effort against infectious disease. Nature
may have the power to create a pandemic—but together we have the power to
prevent it, to stop it, to overcome it, to cure it. And there is no time
like the millennium. For today, history and human progress have created an
"ironic contradiction" in the fight against infectious disease: some of the
same forces that invite pandemics can also be harnessed to fight pandemics.
With the globalization of travel and trade, immigration, communication, and
industrialization, we have a smaller world with porous borders. Nations are
more interconnected, people are more interdependent, and humanity is less
divided by what the Indian poet Tagore called our "narrow domestic walls."
So the bad news is that we have fewer barriers against the spread of
infectious disease; yet the good news is that those fewer barriers mean new
avenues to progress and the potential for sharing information and efforts
to stop infectious disease.
We now have the power to push infectious diseases off the world stage but
only if governments, world health organizations, the private sector,
scientists, and researchers work together with a global strategy. How do we
successfully wage this global battle against infectious disease? The answer
lies in what we can learn from the 1918 pandemic; it provides three
important lessons—challenges for all of us.
The first lesson is that we must assume it could happen again. Influenza
pandemics have regularly swept the world every 10 to 40 years, and it has
been 30 years since the last influenza pandemic, Hong Kong flu, killed
700,000. Nature is creative, and the flu has great potential for mutating.
If a strain changes dramatically, we could suddenly have a virus for which
we may have no immunity, no vaccine, and no cure. The threat is not just
the flu—the spectrum of new infectious diseases is constantly expanding,
while old diseases, such as TB, have evolved into entirely new killers
because they developed antibiotic resistance.
The advent of antibiotics in the 1940s was one of the chief reasons we
began to defeat infectious disease. However, almost as soon as antibiotics
were available, microbes mutated and developed resistance. In the 1950s to
1970s, we produced so many new antibiotics that there was always an
alternative medication; today, the flood of new antibiotics has diminished
to a trickle, while the microbes have continued to grow resistant.
Antibiotic-resistant bacteria are becoming more common in hospitals and
among patients with depressed immune systems. In Japan in 1996 and in the
United States last year, we started to see a strain of staphylococcus
infection, the most common hospital-acquired infection, which could
sometimes withstand vancomycin—our most potent treatment. But almost
simultaneously, the first antibiotic to fight a new generation of "super
bugs," Synercid, won limited approval from a Food and Drug Administration
(FDA) advisory panel. If it wins full approval, it will be the first drug
in a new arsenal of weapons. FDA continues to work with drug manufacturers
to bring new antibiotics to market as safely and rapidly as possible.
Antibiotic resistance is not just a medical problem; it is also a
behavioral problem. Patients too often demand antibiotics for every
illness—even for viral infections (like the flu) that do not respond;
patients often do not finish the course of medication, allowing the
remaining bacteria to develop resistance; many doctors overprescribe; and
the pharmaceutical industry has limited its antibiotic development because
of cost. The widespread use of antibiotics in farm animals may also be
helping the spread of drug-resistant genes. Given the consequences, we must
act now to combat the diminishing effectiveness of antibiotics. That is why
CDC is strengthening surveillance and implementing education campaigns
about the problem, why the National Institutes of Health (NIH) is studying
resistance, and why FDA is promoting judicious antibiotic use. But this is
not a job for government agencies alone. Each and every one of us who
understands the risks needs to spread the message that antibiotics are
being misused, abused, and overused.
The next pandemic could also result not from a mutating bug or ineffective
antibiotics but from an act of bioterrorism. Whether bioterrorism is state
sponsored or undertaken by a lone terrorist, it is not just a problem for
the military or law enforcement; it is also a challenge for the entire
public health community. If a specific threat is issued—perhaps someone
claims to have released a toxic agent in a public place—trained public
health officials must first verify that an incident has occurred. They may
need to decontaminate the area, identify exposed populations, and deliver
preventive measures and treatments. Too often, a threat is not issued, no
warning is given. In such a situation, public health officials must first
quickly determine the deadly agent, the route of exposure, and the likely
source.
The U.S. Department of Health and Human Services (DHHS) is coordinating
with our partners in other agencies and the military to ensure the proper
training of state and local health officials, the availability of vaccines
and drugs, and the enhancement of our surveillance capacity and expertise.
There is also an administrationwide effort to train emergency response
teams and health-care providers in 120 cities. We must enhance our ability
now to address the growing threat of bioterrorism.
The second lesson concerns preparation for a potential pandemic. We cannot
wait until the next deadly microbe appears on the world stage. Therefore,
since 1993, HHS has been leading a federal, state, and local effort to
develop a "pandemic influenza plan." As a result of the avian flu episode,
we have sped up the process to complete the plan and pursue its full
implementation. Meanwhile, CDC is studying the impact of antiviral
medications and alternative ways to produce vaccines. NIH is working with
the pharmaceutical industry to develop and test innovative vaccines,
including a nasal spray that delivers an inoculation dose of the virus. FDA
is issuing new drug permits for experimental influenza vaccines. With new
viruses knocking at the door, we cannot afford to be caught unprepared.
Because only in the movies can we save the world from a deadly disease in
just 24 hours.
We need commitment in responding to all emerging infectious disease. We
need a worldwide "surveillance and response network" that can quickly
identify and stop an outbreak. We have already laid the groundwork for such
a system with bilateral and multilateral talks on disease monitoring with
our partners in Europe, Japan, Asia, and Africa. For example, at the Denver
Summit in 1997, the group of eight industrialized nations, including the
United States, pledged to help develop a global disease surveillance
network and coordinate an international response to infectious disease.
Working through the Trans-Atlantic Agenda with the European Union (EU), the
United States and EU countries have begun to share surveillance data on
Salmonella infections. Additionally, through the U.S.-South Africa
Bilateral Commission, our two countries are training health personnel in
South Africa in surveillance and applied epidemiology. I look forward to
working closely with WHO to further globalize our approach to surveillance
and response.
U.S. agencies are already supporting the efforts of WHO to improve
communications networks and to build regional centers for monitoring
disease. CDC and WHO jointly run 12 world monitoring stations for the flu
alone. Perhaps the best example of the kind of monitoring and surveillance
system needed worldwide is the excellent system that stopped the avian flu
outbreak in Hong Kong. On a routine basis, officials collect throat swabs
from people with flulike symptoms. The samples are analyzed, and if
suspicious, they are immediately sent to CDC, which functions as one of the
WHO International Reference Laboratories for East Asia. When the first
known case of avian flu was diagnosed in a 3-year-old boy, warning bells
went off immediately. When a second case appeared in November, health
officials around the world went on alert, and a team from CDC left for Hong
Kong. Over the next 2 months, work continued to define the extent of the
outbreak, including who was becoming ill, why they were becoming ill, and
whether the virus could spread from person to person and cause a pandemic.
The slaughter of more than one million chickens seems to have halted the
virus at least for now.
Hong Kong's surveillance system proved that early detection of infectious
diseases can prevent their spread. David Heymann of WHO once asked a
provocative question: What would have happened if we had had an excellent
surveillance system in place in Africa when the AIDS outbreak first
occurred? Perhaps we could also have halted that virus in its tracks.
Perhaps we would have spared ourselves the second great pandemic of the
20th century. AIDS taught us that regardless of a person's sexual
orientation, color, wealth, or home, if we hesitate in our fight against
infectious diseases and fail to detect and track them early, they will
eventually affect us all.
We cannot simply deal with each potential pandemic as it arises. We must
also look over the horizon and seize new possibilities to head off
infectious diseases before they can occur. We must fully harness this
golden age of global telecommunications (from satellites to the Internet)
to create a truly global surveillance and monitoring network and find new
ways to prevent, stop, overcome, and cure infectious disease. That is one
of the reasons that President Clinton proposed the 21st Century Research
Fund—a historic national effort to spur the best minds of this generation
to unlock scientific discoveries, unravel scientific mysteries, and uncover
scientific advances. Today, the pace of medical discovery is not limited by
science or imagination or intellect but by resources. Thus, the research
fund will provide a US$1.1 billion budget increase for NIH next year. It is
the first down payment on an unprecedented 50% expansion of NIH over the
next 5 years. This funding will enable NIH to do more to develop new ways
to diagnose, treat, and prevent disease. We are also seeking a boost in CDC
funding to step up our ability to identify and investigate infectious
disease outbreaks, including foodborne outbreaks. CDC will play a key role
in a new initiative by the U.S. Agency for International Development to
develop programs in targeted countries to fight the growing threat of
bacterial resistance, TB, and malaria. This new American investment in
fighting infectious disease will not only pay off in America, because in
this world without borders, a discovery by any one nation will benefit us
all and brings us a little closer to preventing the next pandemic.
The third lesson of the great pandemic of 1918 is that we have the power to
prevent the next pandemic and defeat emerging infectious diseases, but only
if our nations step up the fight together. Because diseases recognize no
borders, in our fight against them, neither can we. Or as Dr. Bruntland of
WHO has stated, when it comes to public health, "solutions, like the
problems, have to be global in scope." That is why U.S. and Japanese
scientists have held three international conferences together on infectious
diseases and research. It is why some members of the Asian-Pacific Economic
Cooperation Area, including Thailand, Indonesia, and the Philippines, have
developed a communications network to track cases of multidrug-resistant
TB. And it is why CDC, FDA, and other U.S. agencies are providing
assistance to the Russian Federation and the Newly Independent States,
which have faced a large increase in infectious disease in the post-Soviet
era.
If we truly want to end the threat of infectious diseases, we must do even
more together. We must inject into global gatherings—no matter where they
are, no matter what the subject—the urgency of working together to defeat
infectious disease. We must never let research into infectious disease
become a forgotten step-child. We must continue to invest in vaccine
research and development and ensure that preventive vaccines are available,
affordable, and effective everywhere. We must work with all our partners in
the private sector to ensure that drugs, vaccines, and tests are available
during an infectious disease emergency. We must ensure that all urban
populations have access to essential facilities, especially clean water,
because vaccines and medicines can do little if water is unclean. We must
work together to deal with urban overcrowding, poverty, and poor
sanitation, which are spreading infectious disease in many parts of the
world. Finally, we must pool our greatest resources—our imagination and
intellect—to fight this collective fight. For as Joshua Lederberg once
noted, "Pitted against microbial genes, we have mainly our wits."
Let us pit our wits (and our will) to this battle, together, to heed the
lessons of the great pandemic and so ensure that it does not happen again,
that we are prepared, and that we always work together. If we do, our
children—the children of the millennium—will remember the 21st century as a
time of health and hope, a time of promise and possibility, a time of
medical miracles and scientific marvels. I have absolutely no doubt that we
can do it, that we must do it, that we will do it.
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Effective Global Response to Emerging Infectious Diseases
Claire Broome
Centers for Disease Control and Prevention, Atlanta, GA, USA
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To discuss the global efforts needed to detect and control emerging
infections, I will begin with a personal experience. In 1987, a large
epidemic of meningococcal meningitis occurred during the haj, the annual
pilgrimage of Moslems to Mecca. The Centers for Disease Control and
Prevention (CDC) sent a team of epidemiologists and laboratorians to
Kennedy Airport to meet the thousands of pilgrims returning to the United
States. Returning pilgrims were given chemoprophylaxis; nasopharyngeal
cultures showed that 11% of the pilgrims carried the epidemic strain of
group A Neisseria meningitidis, the causative agent. Only 25% of the
returning pilgrims were intercepted and treated; thousands of others
dispersed throughout the country (presumably with the same 11% carriage
rate of this highly virulent strain). Were U.S. surveillance systems
adequate to rapidly detect any subsequent outbreaks? We were completely
dependent on local physicians to diagnose cases, on laboratories to isolate
and serotype the organism, on the notification systems to inform the state
and federal agencies. In this instance, the United States was fortunate and
did not see any secondary outbreaks. Other countries were not so fortunate;
large epidemics occurred in Chad, Kenya, and Tanzania as a result of the
same virulent clone of N. meningitidis. The importation of this epidemic
clone illustrates the central importance of local capacity to diagnose,
report, and control emerging infectious diseases.
A more recent example is the 1997 influenza H5N1 outbreak in Hong Kong: the
outbreak illustrates what systems are needed to detect a new organism and
to respond appropriately. First, the Hong Kong public health system had to
have the capacity to isolate the organism and to recognize that it was not
an ordinary influenza strain. Because infections emerge at the local level,
the capacity to detect new threats when they arise should be available
throughout the world. Secondly, the specialized diagnostic reagents had to
be available and the reference laboratories had to be able to make a
definitive identification, not just of that initial strain, but of the
hundreds of other strains evaluated. In this case, H5 reagents (the result
of National Institutes of Health [NIH] research) had been distributed (by
CDC) to reference laboratories internationally. The capacity to respond to
potential outbreaks with expert epidemiologic investigation also had to be
in place. The team that went to Hong Kong consisted of epidemiologists,
laboratorians, a public affairs specialist, and an expert in animal
influenza. The team worked closely with Hong Kong colleagues to detect new
cases by implementing an enhanced surveillance system. They targeted not
only hospitals but also outpatient settings. Most importantly, they
designed studies to rapidly determine whether the strain could be
transmitted from human to human. Would the H5N1 isolates share the
pathogenic potential of human influenza, which is so readily transmissible
from human to human, or was this strain relatively limited in its ability
to spread? The kind of rapid but rigorous epidemiologic studies undertaken
by the outbreak response team were invaluable in answering this question;
fortunately, the strain had limited potential for human-to-human
transmission. Still, we cannot become complacent; given the genetic
recombination potential of influenza viruses, we need to maintain and
enhance our surveillance systems worldwide.
Through the U.S. emerging infections initiative, the number of laboratory
surveillance sites supported to look for new influenza strains has been
increased. In China, sites had been expanded from 6 to 12, which improved
the ability of the World Health Organization (WHO) system to monitor
evidence of dissemination of this strain on the Chinese mainland. Through
the CDC WHO Collaborating Center on Influenza, we made diagnostic kits
based on the NIH H5 reagents available to reference laboratories around the
world so that many different areas can detect H5N1 should it emerge. At the
same time, the WHO Collaborating Center was actively engaged in training
activities.
The H5N1 example shows that we are somewhat better able to deal with
emerging infections in 1997 and 1998 than we were in 1987. The example also
underscores what is needed: dramatically strengthened local surveillance,
including both laboratory and epidemiologic capacity; commitment on the
part of local governments; and a strong collaborative international
research and response system.
Two other areas of international capacity development contribute to effective
response to emerging infections. The first is Field Epidemiology Training
Programs. These programs operate on the assumption that the best way to
develop epidemiologic capacity in a country is to train local professionals who
are committed to continuing to work with the government in surveillance,
outbreak response, epidemiology, and other aspects of public health
management.
Field Epidemiology Training Programs have been developed in 17 countries.
These programs are now planning to create an executive secretariat to
facilitate collaboration and provide regional expertise. WHO and CDC are
working with these countries to ensure necessary support and coordination
with international surveillance. The second area is communication systems.
The Internet globally facilitates our ability to share technical and
surveillance information.
We are better able in 1998 to address the threats of emerging infections,
but we are by no means fully prepared. We must have the capacity to
identify new or reemerging threats and to respond successfully. We need to
be creative and efficient in identifying necessary resources; for example,
the polio eradication program has developed a global network of
laboratories and is strengthening the surveillance systems needed to
identify poliomyelitis cases. Eradication activities also contribute to
health capacity development, and the laboratory and surveillance capacities
created for polio eradication should also be useful in detection of and
response to emerging infectious diseases. Many other creative approaches
and collaborations are needed for an effective global response to whatever
our microbial adversaries may produce.
[photo]
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Addressing Emerging Infectious Disease Threats – Accomplishments and Future
Plans
James M. Hughes
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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In 1962, Sir McFarland Burnet wrote, "One can think of the middle of the
20th century as the end of one of the most important social revolutions in
history—the virtual elimination of the infectious disease as a significant
factor in social life" (1). This statement is at the core of many years of
neglect of infectious diseases—it represents complacency with a capital "C,"
and we are now paying the price.
Infectious diseases, the leading cause of death worldwide (2) and the third
leading cause of death in the United States, have returned with a vengeance
(3). Between 1980 and 1992, infectious disease deaths increased by 58% (39%
after age adjustment); the major contributors were HIV infection and AIDS,
respiratory disease (primarily pneumonia), and bloodstream infection.
In 1994, the Institute of Medicine published Emerging Infections: Microbial
Threats to Health in the United States (4). This report broadly defined as
emerging "new, reemerging, or drug-resistant infections whose incidence in
humans has increased within the past two decades or whose incidence
threatens to increase in the near future." This report, which detailed the
factors involved in emergence, reminds us that we live in a global village.
Spurred on by the Institute of Medicine's report and by outbreaks of
Escherichia coli O157 (January 1993), cryptosporidiosis (April 1993), and
hantavirus pulmonary syndrome (May 1993), the Centers for Disease Control
and Prevention and its partners produced a strategic plan for addressing
emerging infectious diseases (5). The plan focused on increasing
surveillance and response capacity; addressing applied research priorities;
strengthening prevention and control programs; and repairing the public
health infrastructure at local, state, regional, national, and global
levels. Incremental implementation of this plan is ongoing. An update plan
will be published in the fall of 1998.
Addressing Emerging Infections in the United States: Implementation of
CDC's Plan
Emerging Infections Programs
Seven Emerging Infections Programs have been established through
cooperative agreement awards (California, Connecticut, Georgia, Maryland,
Minnesota, New York, and Oregon). These programs share core projects on
invasive bacterial and foodborne diseases. The California program is
focused on the San Francisco Bay Area. Four of the seven programs also
focus on identifying the causes of unexplained deaths and severe illnesses
in previously healthy persons ages 1 to 49 years.
Epidemiology and Laboratory Capacity Cooperative Agreements
Thirty awards established cooperative agreements with 28 states and two
large cities (Los Angeles and New York) (Figure). Funds are used in
different ways in different locales, but each recipient works toward
strengthening infectious disease surveillance capacity and improving
laboratory capacity and the reporting and analysis of infectious
disease surveillance data. In addition, CDC has established three new
provider-based sentinel surveillance systems with several partners. One
network is based in emergency departments in academic medical centers
(Emergency ID Network); a second, involving infectious disease clinicians,
is in collaboration with the Infectious Diseases Society of America; and
the third involves collaboration with the International Society of Travel
Medicine (Geo-Sentinel), which involves travel medicine clinics in the
United States and other countries.
[Fig] Figure. Epidemiology and laboratory capacity cooperative agreements
(shown in gray).
The National Food Safety Initiative
Because of inadequate foodborne disease surveillance in the United States,
the safety of the food supply could not adequately be assessed. Six million
to 81 million cases have been estimated (M. Osterholm, unpub. data). Food
Safety from Farm to Table (6), released in 1997, underlines the Clinton
Administration's commitment to improving food safety.
The National Molecular Subtyping Network
The national molecular subtyping network (7) for foodborne disease
surveillance (PulseNet) represents a model of disease surveillance that
takes into account the globalization of the world's food supply. During the
summer of 1997, the state public health laboratory in Colorado using
molecular fingerprinting techniques (pulsed-field gel electrophoresis)
recognized a cluster of 15 cases of E. coli O157:H7 infections from widely
scattered areas in the state (8). Rapid epidemiologic investigation
implicated undercooked ground beef from a single company, resulting in the
recall of 25 million pounds of ground beef and the closing of the plant
that produced it. This outbreak illustrates the critical role of public
health laboratory capacity and rapid public health action in outbreak
detection and response. Before the recent advances, this outbreak probably
would not have been detected.
The Emerging Infectious Diseases Laboratory Fellowship Program
In an effort to strengthen public health laboratory capacity, CDC in
collaboration with the Association of State and Territorial Public Health
Laboratory Directors will be providing opportunities for training state
public health laboratory workers (9). Forty-five fellows have participated
in this program. An international track will be inaugurated in the summer
of 1998 with the support of the CDC Foundation and Eli Lilly and Company.
The Emerging Infectious Diseases Journal
To better track trends and analyze new and reemerging infectious disease
issues around the world, CDC established a quarterly, peer-reviewed
international journal (www.cdc.gov/eid/). The journal, a part of the
communications component of the strategy against emerging infections, has
facilitated the exchange and dissemination of scientific information about
these infections.
Future Plans
Antimicrobial resistance, new and reemerging infections, and a strong
public interest in health will demand vigilance, renewed efforts, and
strengthened partnerships in infectious diseases. An update of CDC's
strategic plan along with cooperative efforts across government and private
organizations all over the world will drive future efforts for the control
of new and reemerging infections.
References
1. Burnet M, White DO. Natural history of infectious disease. London:
Cambridge University Press; 1962.
2. World Health Organization. The World Health Report 1997: conquering
suffering, enriching humanity. Report of the Director-General. Geneva,
Switzerland: The Organization; 1997.
3. Pinner RW, Teutsch SM, Simonsen L, Klug LA, Graber JM, Clarke MJ,
Berkelman RL. Trends in infectious diseases mortality in the United
States. JAMA 1996;275:189-93.
4. Institute of Medicine. Emerging infections: microbial threats to
health in the United States. Washington: National Academy Press; 1992.
5. Centers for Disease Control and Prevention. Addressing emerging
infectious disease threats: a prevention strategy for the United
States. Atlanta (GA): U.S. Department of Health and Human Services,
Public Health Service; 1994.
6. U.S. Department of Health and Human Services, U.S. Department of
Agriculture, U.S. Environmental Protection Agency. Food safety: from
farm to table. A national food-safety initiative. A Report to the
President, May 1997. Washington: Government Printing Office; 1997.
7. Stephenson J. New approaches for detecting and curtailing foodborne
microbial infections. JAMA 1997;277:1337-40.
8. Centers for Disease Control and Prevention. Escherichia coli O157:H7
infections associated with eating a nationally distributed commercial
brand of frozen ground beef patties and burgers–Colorado, 1997. MMWR
Morb Mortal Wkly Rep 1997;46:777-8.
9. Emerging Infectious Diseases Fellowship Program. Emerg Infect Dis
1995;1:105.
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Emerging Infections: An Evolutionary Perspective
Joshua Lederberg
The Rockefeller University, New York, New York, USA
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Our relationship to infectious pathogens is part of an evolutionary drama
(1). Here we are; here are the bugs. They are looking for food; we are
their meat. How do we compete? They reproduce so quickly, and there are so
many of them. They tolerate vast fluctuations of population size as part of
their natural history; a fluctuation of 1% in our population size is a
major catastrophe. Microbes have enormous potential mechanisms of genetic
diversity. We are different from them in every respect. Their numbers,
rapid fluctuations, and amenability to genetic change give them tools for
adaptation that far outpace what we can generate on any short-term basis.
So why are we still here? With very rare exceptions, our microbial
adversaries have a shared interest in our survival. With very few
exceptions (none among the viruses, a few among the bacteria, perhaps the
clostridial spore-forming toxin producers), almost any pathogen reaches a
dead end when its host is dead. Truly severe host-pathogen interactions
historically have resulted in elimination of both species. We are the
contingent survivors of such encounters because of this shared interest.
Microbial Resources
Intraclonal Processes
DNA Replication
Microbial intraclonal methods of variation are legion. DNA replication is
error prone, and often the constraints of precise replication are turned
off in the presence of DNA damage or other injury. Microbes often live in a
sea of mutagens, chemical and physical. If we go out in the sun, our skin
is damaged; in microbes, UV irradiation goes unimpeded to the very core of
their DNA. Those that are not killed are rapidly mutated.
RNA Replication
RNA replication is particularly error prone. There are no editing
mechanisms for examining the fidelity of replication; therefore, the
concept of the quasispecies swarm was recently generated. For many RNA
viruses, retroviruses in particular, the rates of mutation are so high that
to a close approximation, every particle is genetically different (in at
least one nucleotide) from every other particle. They are rapidly evolving
as swarms of genotypes, no single genotype being totally representative.
Natural selection plays a substantial role. The role of cooperativity in
infection of these viruses, particularly among retroviruses and HIV, has
not been adequately investigated. Rous sarcoma virus is a case in point. It
may be difficult for a single particle, many generations removed from the
original competent infector, to consummate an infection by itself, but it
can be complemented by other helper viruses present in the same cell.
Haploid Organisms
Most of the organisms we are dealing with are haploid, so they have no
delay in expressing new genetic factors. The prompt expression may
potentially augment cumulative genetic alterations, but in the short run, a
resistance mutation will manifest itself almost immediately and will be
subject to natural selection very promptly. Multicopy plasmids, which would
behave differently, are exceptions.
Phase Variation
Phase variation occurs in almost every pathogenic bacterium, in malaria
parasites, in trypanosomes, and in Borrelia. Changes that appear to be
mutational, on closer examination turn out to be microbial access to an
archive of genetic information, much of which has been silenced and then
reappears as an adaptive change. The flagellar antigens of salmonella
provide the historic example; they can exist in either so-called specific
phase or group phase, going back to H1 or H2 loci. We now know that they
are the result of silencing one of these loci by the position of a piece of
DNA that can be inverted to move the promoter from one locus to another and
give a very sudden transformation of the serotype from type 1 to type 2.
This is a completely reversible phenomenon; the same event can reinvert
that DNA. Many species of site-specific recombinases are capable of
scrambling and rescrambling the bacterial genome in order to silence and
unsilence genes that may be then carried in an archival state. I pondered
why bugs use this mechanism for keeping genes in a cryptic state when gene
expression can be (and often is) regulated in other ways. The simplest
speculation is that phase variation very often entails controlled antigenic
factors. A bug does not want to telegraph to its host in advance that it is
carrying even a tiny relic of an alternative epitope because that will
provoke immunity on the part of the host even before it has undergone that
phase variation.
Genetic factors also control the rates of mutability; whether these factors
do or do not directly influence adaptability to virulence is controversial.
Preliminary reports suggested that virulent bacteria had a higher incidence
of mutators. We now realize that mutators are quite prevalent, and
therefore bacteria are constantly facing environmental challenges.
Interclonal Processes
Recombination mechanisms are quite promiscuous. Conjugation, which can
occur between bacteria of widely varying kinds, is most often recognized by
plasmid transfer and every now and then by mobilization of chromosomes.
Conjugation can even occur across kingdoms, between a bacterium and a
yeast, or between a bacterium and a plant. In the case of the
rhizobium-like parasite, the crown gall bacterium, genetic material is
transferred from the bacterium into the chromosomes of the host plant.
Similar phenomena probably occur in eukaryotic infections. Some genes in
viruses and bacteria almost certainly were of eukaryotic origin. Some
bacteria can deliver DNA intercellularly to their host animals.
Plasmid interchange (movement of tiny bits of DNA from one species to
another) is not just a laboratory curiosity; it is the mechanism for rapid
spread of antibiotic resistance from widely different species, one to
another. It adds even greater cogency to our concerns about the less than
optimally advantageous use of antibiotics (e.g., in animal husbandry). The
mechanisms exist to make it easy not only for single antibiotic resistance
but whole blocks of resistance to be moved from one bacterium to another.
Host-Parasite Coevolution
Microbes' shared interest in our survival will dominate the overall picture
of their evolution. Can this help us predict the outcome of the balance
between the host and the pathogen? The possible outcomes are so divergent
that it is very difficult to predict in detail what is going to happen in
any particular confrontation.
The long-term trend is coadaptation, in which the host acquires factors for
resistance and the parasite acquires factors for mitigation and longer
survival of (and thereby in) the host. These factors may be genetic
mutations, which will certainly be selected.
Other factors include human cultural changes, such as hygienic procedures.
The human species outdoes all other species in adopting behavior that is
self-destructive rather than self-protective. I am not convinced that every
nuance of human behavior has been specifically evolved. Most of our
behavior, even the maladaptive self-destructive kind, is learned: the pity
and the hope of our species.
Pathogens find it to their advantage to mitigate their virulence, provided
they can do so without compromising their livelihood. That is the tightrope
they walk. Rhinovirus, the agent of the common cold, is an extremely
successful pathogen. We do little to get rid of it. We go to work and
school with our runny noses. The virus has a number of adaptations
(including the very moderation of its disease process) that tend to
facilitate its spread. I worry that a rhinovirus may some day mutate into a
somewhat more virulent form, given that it is capable of very rapid spread.
Evolutionary Strategies
The parasite's dilemma is that if it proliferates rapidly, it may kill the
host; that would be a winning strategy if transmission were easy, vectors
readily available, the host's behavior obliging, and mosquitoes abundant
for high-density spread. Such circumstances are present in northwest
Thailand where Plasmodium falciparum would be unlikely to survive for very
long (because of its profound effects on its host) if the density of spread
to new hosts were not favorable. In modern hospitals, the mosquitoes are
health-care attendants who inadvertently facilitate the transfer of
infection from one patient to another.
Toxins
It is a wonder that the inexhaustible reservoir of potent toxins has not
spread much further. Botulinum toxin, one of the deadliest compounds, is
produced in abundance by Clostridium botulinum, whose spread to other
organisms and potential for becoming a major public health threat can
easily be imagined. Why is this toxin so confined? The underlying biologic
mechanisms are not confining it; rather, its lethality keeps it under
control. The microbe kills its host rapidly, and if it cannot continue to
multiply even in the dead host, it reaches a dead end.
In specific physiologic circumstances, these rules of natural selection
might not apply. Escherichia coli O157 is a case in point. O157 has little
to do with E. coli; it is a shigella with a little cloak of E. coli
antigens. O157 should not be used as the sole diagnostic criterion for the
spread of shigelloid disease. The toxin genes can inhabit other vectors.
The ecologic implications of its human and bovine virulence are not clear.
Perhaps polymorphism (changes in bacterial genotype) alters its virulence
in human and bovine species. The human loop is quite incidental to its
overall survival, as far as we know. The attack rate in humans is only 1%.
How has E. coli O157 evolved? We understand that as poorly as we understand
the sporadic emergence of Legionella from the soil into our air-conditioner
ducts.
Proliferation Rate
If the parasite adopts another strategy and proliferates slowly, we have an
evolutionary mechanism in which our own immune system is looking for
deviants; this mechanism will be presenting new epitope receptors waiting
to be stimulated. Most acute infections produce a full immune response at a
humoral and a cellular level within a week or 10 days. So the microbe that
proliferates slowly is laying the groundwork for its own vulnerability
unless it adopts some further tactics (e.g., phase variation, stealth
tactics, antigenic mimicry, exploiting the autotolerance that the host
needs to survive its own immune system). Parasites also compete with
commensals, with probiotic organisms. This is where HIV runs into severe
trouble. Left to its own devices, HIV would not kill its host; but by
knocking down the host's immune system, the virus opens the door for other
organisms, including commensals, opportunists that can thrive only when the
immune defenses are attenuated.
Symptoms
Vectors are rarely symptomatic, almost never severely symptomatic. The
plasmodium would not benefit from killing the mosquitoes that transmit it.
If a rabid dog can be considered a vector, its behavioral anomaly
illustrates another adaptation that serves the purposes of the parasite.
This line of thinking, what some people have called evolutionary
medicinecall it common senseleads us to look at symptoms. To what extent
should we be treating them? Some we treat because they are
life-threatening. But is fever, for example, a host defense? Is it a mode
of bacterial attack? Is the bacterium or virus producing pyrogens because a
higher temperature will promote its own replication? Are pyrogens just side
effects of other evolutionary adaptations that have not come to
equilibrium? It is hard to avoid models that assume equilibrium; few
complex physiologic systems are so obliging. We should question symptoms
from an evolutionary perspective. How did they come to be there? This
approach may open the door to new avenues of thought in examining the
disease process. Cough, diarrhea, or hemorrhage may serve the purposes of
the parasite; even so, we may still have to treat hemorrhage, but how far
should we go in treating cough? On the one hand, if not too severe, cough
may eliminate some of the infectious load from the body; on the other hand,
cough generates an aerosol that further disseminates the organism. Cough
may have to be treated as a public health measure as much as a therapeutic
measure. Diarrhea is another example; it may be a way of eliminating the
parasite or a special adaptation enhancing dissemination.
Other symptoms (malaise, headache, pain, itching) probably have different
answers. Pain is a puzzling symptom, which plays an indispensable role by
drawing attention to a disease. Once the disease is acknowledged, there is
no reason in the world not to treat pain. Yet I know of no infection (other
than chronic leprosy) that induces anesthesia. It would seem to me that a
microbe bent on thriving would impart a sense of euphoria (rather than
pain) to its host; we would welcome it and infect ourselves with it.
Analgesia may be the eventual moral hazard of biotechnology, the
internalized moonshine still or poppy patch.
The ultimate symptom, death of the host, is almost never to the advantage
of the parasite. Death signals a breakdown in the equilibrium (the contract
between parasite and host) that could have had a better outcome had both
sides been more witting.
Zoonotic Interactions
Many lessons of evolutionary relationships come from zoonotic interactions.
Infections that break out of their host of origin often have a very severe
impact on their new host. Hantavirus is an outstanding recent example. The
pathologic processes in the rodent carriers hardly compare with those in
humans. Most zoonotic transfers simply do not work. They are host specific;
many are neutral. Every now and then, a zoonotic transfer has enormously
larger pathologic implications for the host; these are the transfers we
focus on. We presume that the filoviruses and perhaps HIV are in that
category. Many, not all, simian immunodeficiency viruses are perceptibly
less virulent in their natural host than HIV is in humans, perhaps another
example of equilibrium breakdown.
How could the zoonoses be pathogenic when they require so many subtle
adaptations to come into a host and really cause disease? Dozens, if not
hundreds, of bacterial genes would have to work in concert to be pathogens.
Microbes make proteins and carbohydrates, familiar to our systems of
immunity. Therefore, if the parasite does not know how to live in the
earthly host and the host cannot cope with totally alien parasites, we end
up with a wash.
Consider tsutsugamushi fever, scrub typhus. Bangkok is reporting
intermediate levels of drug resistance in Orientalia in tsutsugamushi in
central and eastern Thailand. The life cycle is one of essentially a
hereditary symbiont; the tick is transmitted transovarially and can be
communicated from tick to microbe or humans, where it rapidly proliferates.
Reinfection back to the tick is not of consequence, which must be a fairly
recent spillover of pathogenicity for which there is not ongoing selection.
Nothing in the life history of Orientalia would sustain its pathogenicity
to maintain its high infectivity.
Years ago planetary quarantine became a policy consideration, beginning
with Sputnik in the late 1950s and the early planning of our space program.
Would it be permissible to move contaminated spacecraft from one planet to
another? Certainly proliferating organisms on Earth could be easily carried
to Mars. What would happen if we brought back Mars samples? These
considerations resulted in an international convention for the conservation
of the microbial virginity of celestial bodies. Sterilization protocols
were applied to the Viking Mars spacecraft and by the Russians in the
1970s.
Maternal Immunity
One mechanism of accommodation is not genetic but physiologic: maternal
immunity. The recent outbreak of canine distemper in the lions of the
Serengeti (1) demonstrates a quasihereditary cycle that does not involve
the genes at all but rather is the propagation of maternal immunity,
partial immunity on the part of the offspring, easier adaptation to
infection by the host.
Mitochondriathe Ultimate Pathogens
What are the ultimate pathogens, the ultimate symbionts? The mitochondria.
A bacterial invader probably 2.5 billion years ago got into the first
eukaryotic cells and conferred oxidative machinery. Who is serving whom? We
generally think mitochondria are to our advantage, but think how hard we
work to shovel the coal into the furnace that the mitochondria have
provided in every cell of our body. Symbiosis is a fact of life, not always
friendly or mutually accommodating. In bacteria, plasmids confer great
advantages for some functions, but many plasmids also convey a "leave me
and you die" message. The plasmid encodes simultaneously for a toxin and an
antitoxin but makes sure that the toxin has a longer lifespan. So a
bacterium careless enough to drop its plasmid will suffer. The plasmid has
the long-term advantage of ensuring that only cells able to continue to
proliferate will continue to have the plasmid. So knowing who is serving
whom in these kinds of relationships is very complicated.
Patterns of Evolution
Thanks to the wonders of genomics and DNA analysis, we have a good overall
model of the tree of life and the overall patterns of evolution. By the
criterion of 16S RNA, extraordinary evolutionary changes have occurred
within the multicellular branch, but these changes are not at the level of
fundamental housekeeping machinery; they have to do with growing brains,
eyes, branches, and flowers, incidental items not at the level of cellular
physiology.
Viruses
Where do viruses come from? Certainly in the world of eukaryotic viruses,
no one can say with confidence what the evolutionary provenance is. We
believe that viruses originated from some kind of cellular organelle,
perhaps ultimately from the nuclear DNA, perhaps from the other organelles.
Many of them would have to have undergone enormous changes, and we cannot
say which came from where in any tangible example. This complexity can be
illustrated (in the prokaryotic systems) by the ease with which viral
genomes can be integrated into bacterial chromosomes. These are all
double-stranded DNA bacterial viruses, so they have the same fundamental
structure as bacterial chromosomes. They go in and out with ease and can be
integrated and mobilized, sometimes as viruses, sometimes as bacterial
genes. It is impossible to say which came first. If one could point to an
evolutionary progression of clusters of genes in a bacterium on the way to
generation of a new virus, it would be of some help, but how would one know
it was not the relic of a very old one coming back again? Our most
fundamental knowledge is very primitive.
Prions
Prions offer a new paradigm, much of which we do not understand. Stan
Prusiner has argued that prions are pure proteins. Trying to understand how
a pure protein can propagate confounds our conceptions of the transmission
of biological information. So let us say that prion protein (e.g., scrapie
prion protein) is a conformational modification of a normal protein, prp-c,
coded for by an endogenous gene, a part of the normal genome, not an
essential gene. Infected mice show some functional disorders but can
survive. One might argue that we do worse with this gene than without it as
long as we are susceptible to this modification.
Not much new sequence information is imparted to the normal prion to
convert it to the infective agent. The change may be merely in the prion's
conformation. We must consider other mechanisms that might cause that same
conversion.
The rare nonfamilia incidence of sporadic Creutzfeldt-Jakob disease (CJD)
poses a possible example, although it is difficult to exclude some contact
with prions in individual cases. We might watch for CJD-like disease as an
incident to other kinds of toxic insults. One implication of the
protein-prion model, not discussed hitherto, is that conformer alterations
may ensure from chemical or physical trauma to preexisting prp-c; heat,
toxins, side effects of other infections are candidates (2). Let us
carefully label this as wild speculation, pending badly needed assays for
this conformer-altering capacity. Other protein-aggregate or amyloid-based
diseases (like Alzheimer's) likely have a nucleating episode in their
pathogenesis, even if there is no means of contagion from one person to
another. At least in the pancreas, amyloid aggregation is a side effect of
protein injury by glycation (3).
Emerging Pathogens
What are we going to do about new, mutant, and recombinant pathogen
strains? What can we anticipate about new major outbreaks? How should we be
defending ourselves? The good news of course is the wonderful technology in
the offing, one marvelous innovation after another in every field of
prophylaxis, vaccines, understanding of pathogenic phenomena. The genomics
work on bacteria is paying off and may even justify the overall project of
human genomics all by itself with its insights into microbial evolution and
potential targets for new discoveries in disease management.
At a very high strategic level, we have the basic knowledge to control
foodborne epidemics, waterborne epidemics, and fecal-borne diseases. At a
technologic level, even sexually transmitted diseases can be controlled.
One neglected medium is air. Can we do as well in preventing airborne
transmission? Effective control may come down to something as elementary as
a face mask like that worn by police in 1918. Control of even a vicious
airborne epidemic like influenza should not be above our technical
capability. Tens or even hundreds of millions of lives might be at stake
over such elementary matters.
The introduction of a new hemolysin into existing anthrax strains in a
demonstration of their pathogenicity in golden hamsters (4)required
additional epitopes to vaccinate those hamsters against this anthrax. This
first example of an artificially contrived new human pathogen illustrates
additional challenges in the fight against emerging infections.
Natural infection and disease are enough of a challenge and should not be
compounded by human-made agents of death. Biological warfare cannot be
endured and must not be tolerated.
Dr. Lederberg, Nobel laureate in physiology or medicine, is a research
geneticist, Sackler Foundation scholar, and president emeritus at the
Rockefeller University. Dr. Lederberg currently conducts research on
genetic exchange mechanisms in bacteria.
References
1. Lederberg J. Infectious disease as an evolutionary paradigm. Emerg
Infect Dis 1997;3:417-23.
2. Causette M, Planche H, Delepine S, Monsan P, Gaunand A., Lindet B. The
self catalytic enzyme inactivation induced by solvent stirring: a new
example of protein conformational change induction. Protein Eng
1997;10:1235-40.
3. Kapurniotu A, Bernhagen J, Greenfield N, Al-Abed Y, Teichberg S, Frank
RW, et al. Contribution of advanced glycosylation to the
amyloidogenicity of islet amyloid polypeptide. Eur J Biochem
1998;251:208-16.
4. Pomerantsev AP, Staritsin NA, Mockov YV, Marinin LI. Expression of
cereolysine AB genes in Bacillus anthracis vaccine strain ensures
protection against experimental hemolytic anthrax infection. Vaccine
1997;15(17-18):1846-50.
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Emerging Infectious Diseases: A Brief Biographical Heritage
D. Peter Drotman
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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The concept that infectious (and other) diseases emerge and reemerge is not
new, and neither is the search for causes of disease emergence. However,
societies frequently overlook or forget that microbes evolve, adapt, and
emerge in response to nonmicrobial and even nonbiologic changes in the
physical and social environment. Sometimes we need to be rudely reminded of
this lesson. Two scientists who have delivered such reminders, both in the
form of landmark reports, are Rudolf Virchow, a 19th century German
pathologist, statesman, and anthropologist, and Joshua Lederberg, the
American microbiologist who coined the phrase "emerging infectious
diseases" within the last decade (Photo). We owe much to the pioneering
vision of these scientists.
[Photo/Fig] Rudolf Virchow and Joshua Lederberg
Infectious diseases have been emerging for at least as long as humans have
inhabited the earth. Every student of microbiology, medicine, and public
health learns about the triangle of host, environment, and agent; what is
not clear is how the three change over time, often in response to changes
in another side of the triangle. Factors that influence such changes do
evolve, but many are surprisingly constant. How easily and often some of
these factors are overlooked is often both consequential and tragic; a
historical example illustrates this point.
Rudolf Virchow, the founder of cellular pathology, wrote the first textbook
in that field and established the principle that disease results from
disturbed cellular function. As a young physician and anatomic pathologist
in Berlin, he was assigned by the central government to investigate an
epidemic in Upper Silesia, a sector of the Prussian Empire populated by a
Polish-speaking minority. He completed the field portion of his
investigation on March 10, 1848 (exactly 150 years before the International
Conference on Emerging Infectious Diseases). The report he wrote was
remarkable.
Even though Virchow was working before the germ theory of disease was
accepted, at a time when disease causation was highly debated and microbes
were not well described, he seems to have correctly diagnosed typhus (or possibly
relapsing fever) as the cause of the Silesian epidemic (1). Even though
Virchow's diagnosis cannot be confirmed, it is consistent with clinical
descriptions and epidemiologic inference. He clearly demonstrated that the
conditions and vectors for typhus and relapsing fever (famine and malnutrition,
humid climate, poor housing, poverty) were present in Upper Silesia in 1847
to 1848. The agents that cause epidemic louse-borne typhus fever (Rickettsia
prowazekii) and relapsing fever (Borrelia recurrentis) were not described
until many years later.
[photo]
Virchow's report was a scathing criticism of the Prussian government, which
he squarely blamed for the epidemic. Virchow considered the Silesian
outbreak investigation a defining episode in his life and career, so when
the government largely ignored the report and his recommendations (Table
1), he became a passionate voice in politics, albeit in a minority role. He
died in 1902, a revered scientist with a lifetime of magnificent
achievements, but also with desires to have done more to improve public
health and social conditions. We still have a lot to learn from Virchow's
life and work.
Joshua Lederberg was awarded the Nobel Prize for medicine in 1958 for his
discoveries concerning genetic recombination and the organization of the
genetic material of bacteria. He is President Emeritus of The Rockefeller
University in New York, a member of the Institute of Medicine, an advisor
to presidents, and a 20th century Rudolf Virchow. Like Virchow, Lederberg
recognized that microscopic changes make much larger differences,
particularly when viewed in the context of global changes. Like Virchow, he
coauthored a prescient report that associated a pressing health emergency
with larger social, political, and environmental changes. The similarities
between the two reports are striking (Tables 1, 2). Each regarded control
of diseases as primarily social, political, and environmental. We overlook
this common theme at our collective peril.
Unlike Virchow's report, the words of Joshua Lederberg are being translated
into actions. Those actions can be spurred by disseminating information and
building partnerships to effectively address the ongoing threat of emerging
infectious diseases.
Table 1. Virchow's recommendations to the Prussian government regarding
the typhus epidemic in Upper Silesia, 1848 (2)
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Political reform and local self-government, including local coordination
of relief efforts
"Education, with its daughters, liberty and prosperity" (3)
Economic reform
Agricultural reforms, including development of cooperatives
Building of roads
Acceptance of Polish as an official language (while most Silesians spoke
Polish, nearly all the physicians and school teachers assigned by the
central government spoke only German)
Separation of church and state (he criticized the Catholic hierarchy) (4)
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Table 2. Factors in disease emergence—The
Institute of Medicine's 1992 report on emerging
infections (5)
-------------------------------------------------
Human demographics and behavior
Technology and industry
Economic development and land use
International travel and commerce
Microbial adaptation and change
Breakdown of public health measures
-------------------------------------------------
References
1. Eisenberg L. Rudolf Ludwig Karl Virchow: Where are you now that we
need you? Am J Med 1984;77:524-32.
2. Silver GA. Virchow, the heroic model in medicine: Health policy by
accolade. Am J Public Health 1987;77:82-8.
3. Virchow RL. Report on the Typhus Epidemic in Upper Silesia. Translated
in: Rather LJ, editor. Rudolf Virchow: Collected Essays on Public
Health and Epidemiology, 2 vols. Canton (MA): Science History
Publications 1985:311.
4. Taylor R, Rieger A. Medicine as a social science: Rudolf Virchow on
the typhus epidemic in Upper Silesia. Int J Health Services
1985;15:547-59.
5. Lederberg J, Shope RE, Oaks SC, editors. Emerging Infections:
Microbial Threats to the United States. Washington: National Academy
Press, 1992.
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New and Reemerging Diseases: The Importance of Biomedical Research
Anthony S. Fauci
National Institutes of Health, Bethesda, Maryland, USA
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A generation ago, it was suggested that the threat of infectious diseases
would soon become an artifact of history. Today, as we approach the new
millennium, the folly of this position is increasingly clear. My
87-year-old father recently reminded me of this. In the course of his
lifetime, spent almost entirely in New York City, he has witnessed two
pandemics of extraordinary impact: the global influenza pandemic of
1918-1919, which killed more than 20 million people worldwide, and the
HIV/AIDS pandemic, which began to accelerate in the early 1980s and
continues unabated in some parts of the world. In addition, at least 30
other new and reemerging diseases and syndromes have been recognized since
the 1970s, including liver disease due to hepatitis C virus, Lyme disease,
foodborne illness caused by Escherichia coli O157:H7 and Cyclospora,
waterborne disease due to Cryptosporidium, hantavirus pulmonary syndrome,
and human disease caused by the avian H5N1 influenza virus (Figure 1).
Clearly, we remain vulnerable to new and reemerging diseases.
[Fig]
Figure 1. Examples of new and reemerging diseases.
New diseases are superimposed on endemic diseases such as diarrheal
diseases, malaria, tuberculosis (TB), and measles, which continue to exact
a huge toll. Indeed, malaria and TB, among others, are reemerging in a
drug-resistant form. Today, infectious diseases remain the leading cause of
death worldwide and the third leading cause of death in the United States.
Many pathogens are becoming increasingly resistant to standard
antimicrobial drugs, making treatment difficult and in some cases
impossible. Moreover, chronic conditions generally considered noninfectious
actually have been found to have a microbial etiology.
Awareness of Emerging Infections
The challenges posed by infectious diseases are recognized by the public
and the media, as well as by political leaders and policy makers at the
highest levels of government. There is a growing awareness that we live a
global community, that diseases do not recognize borders, and that the U.S.
public health community has an important role to play in fostering global
health.
The Importance of Research
The infectious diseases community faces a difficult challenge: coping with
ongoing problems such as malaria and TB while preparing for the inevitable
emergence of diseases that are unknown or are recognized but will reemerge
in a more threatening form. Available resources must be maximized by
sustaining and increasing collaboration between federal agencies, academia,
industry, and nongovernmental agencies, all of which play important roles
in the fight against infectious diseases.
Within the federal government, the Centers for Disease Control and
Prevention's (CDC) work in detecting and tracking pathogens is critical,
especially with regard to diseases that have recently emerged or have the
potential for emergence. Equally important, and complementary to CDC's
efforts, is basic and clinical research supported by the National
Institutes of Health (NIH) and other agencies. Historically, basic research
has led to important, often serendipitous, advances that have illuminated
the etiology of sometimes mysterious diseases and facilitated the
development of diagnostics, therapies, and vaccines (Figure 2).
[Fig]
Figure 2. Emerging infectious diseases: a research approach.
At the National Institute of Allergy and Infectious Diseases (NIAID) at NIH,
we have increased funding for emerging diseases from $39.3 million in fiscal
year 1993 to an estimated (president's budget) $85.0 million in fiscal 1999
(Figure 3). Approximately 21% of the NIAID non-AIDS infectious diseases
budget is devoted to emerging infectious diseases.
[Fig]
Figure 3. Emerging diseases funding (National Institute of Allergy and
Infectious Diseases.
With the help of our advisory committees, we have defined five priorities
in emerging and reemerging diseases research: 1) supporting the application
of relevant scientific knowledge and new technologies to the detection,
identification, and interdiction of emerging diseases, by expanding
research on ecologic and environmental factors influencing disease
emergence and transmission; 2) supporting the application of recent
discoveries and new biomedical technologies to the identification,
management, and control of emerging diseases, by expanding research on
microbial changes and adaptations that influence disease emergence; 3)
providing fundamental information for developing prevention and treatment
strategies that can be employed to ameliorate disease impact, by expanding
research on host susceptibility to emerging or reemerging pathogens; 4)
supporting the development and validation of vaccines, therapeutics, and
other control strategies for specific diseases with the potential to emerge
or reemerge; and 5) strengthening the current U.S. research and training
infrastructure for detecting and responding to outbreaks of infectious
diseases.
Among many studies domestically and internationally, NIAID sponsors five
international programs in tropical infectious diseases, most of which have
components both in the United States and in the countries where the
incidence of these diseases is greatest. It is essential to engage
scientists in host countries and work with them collaboratively, both to
tap their expertise as well as to help them build research infrastructure
on their home soil.
Successful Partnerships
The public and private sectors, including government, academia, and
industry, bring complementary skills and perspectives to the research
endeavor. Cross-sector collaboration can yield extraordinary dividends. A
cogent example is the development of protease inhibitors for the treatment
of HIV disease.
After HIV was identified in 1983, researchers funded by NIH and others
began to intensively study the structural and regulatory genes of HIV and
the role these genes and their products play in the replication cycle of
the virus. This work led to an understanding of the importance of the HIV
protease enzyme and methods to express, purify, and crystallize the enzyme.
Building on these findings, researchers in the private sector designed and
produced specific inhibitors of HIV protease and worked closely with the
Food and Drug Administration, NIH, and others to assess protease inhibitors
in clinical trials.
The first of four licensed protease inhibitors reached the market in
December 1995. Given in combination with at least two other antiretroviral
drugs, protease inhibitors dramatically reduce levels of plasma viremia in
a substantial proportion of patients. Both controlled and observational
studies show that these potent regimens can provide a substantial clinical
benefit.
Although drug combinations that include protease inhibitors have helped
many patients, it is far too soon to become complacent or declare victory.
Many patients have not benefited from the new drugs or cannot tolerate
their side effects, and drug resistance will inevitably become more
widespread. The development of the next generation of antiretroviral agents
is crucial and will require the skills of investigators in both the public
and private sectors. However, the cost of antiretroviral drugs will
probably keep them beyond the reach of much of the developing world;
therefore, the development of an HIV vaccine is of paramount importance.
Malaria Initiatives at NIH
Until relatively recently, AIDS was virtually the only emerging disease
with global impact that was widely discussed in the United States; however,
other diseases such as malaria and TB have actually caused more illnesses
and deaths over the past 2 decades.
Malaria kills up to three million persons each year, most of them children
in sub-Saharan Africa. In the past year, NIH has worked with research
organizations and donor agencies from around the world to form a coalition
called the Multilateral Initiative on Malaria. This unprecedented
initiative will enhance international collaborations, encourage the
involvement in malaria research of scientists from malaria-endemic
countries, and identify additional malaria research resources. In addition,
NIH has bolstered its long-term commitment to malaria research.
NIH-supported malaria projects—many in collaboration with other government
and international agencies—include 1) a new repository of materials
available to researchers worldwide; 2) basic, field-based, and clinical
research on all phases of malaria research; and 3) projects to determine
the genetic sequences of important malaria species.
Responding to Avian H5N1 Influenza
An outbreak of avian H5N1 influenza in Hong Kong recently alarmed the
medical community and the world. The multinational response to this
outbreak has involved the close collaboration of many organizations (Figure
4). As part of NIH's long-standing research into respiratory viruses, we
had in our reagent repository the specific antisera needed to quickly
develop test kits that were used effectively by CDC and others for
detecting and tracking the virus. We also have supported the rapid
production of a recombinant vaccine against avian influenza virus for use
in laboratory and health-care personnel at risk. Without a strong research
base, the rapid response to this emergency would not have been possible.
[Fig]
Figure 4. Response to H5N1 avian influenza outbreak in Hong Kong.
Vaccine Development
With avian flu, malaria, AIDS, and other new and reemerging diseases, an
important goal of NIH is the development of vaccines. If just four recently
developed vaccines (hepatitis B, rotavirus, Haemophilus influenzae type b,
and acellular pertussis) were universally administered, more than three
million deaths could be prevented each year.
Historically, scientific advances in microbiology and related disciplines
have driven the development of new vaccines. For example, the
identification of microbial toxins, as well as methods to inactivate them,
allowed the development of some of our earliest vaccines, including those
for diphtheria and tetanus. In the 1950s, new tissue culture techniques
ushered in a new generation of vaccines, including measles, mumps, and
rubella. In recent years we have seen rapid advances in our understanding
of the immune system and host-pathogen interactions, as well as technical
advances such as recombinant DNA technology, peptide synthesis, and gene
sequencing. Each of these has facilitated the development of new vaccines
and vaccine candidates for important pathogens.
Sequence information can be used in many ways and promises to be useful in
identifying antigens to incorporate into vaccines, as well as determining
the factors that influence the antigenicity or virulence of a microbe. The
complete genetic sequences of more than 13 microorganisms have now been
published. More than 60 other sequencing projects for medically important
pathogens, such as Plasmodium spp., Mycobacterium spp., Chlamydia
trachomatis, Vibrio cholerae, and Neisseria gonorrhoeae, are under way.
Conclusion
The importance of basic research to the control of emerging and reemerging
diseases cannot be overemphasized. Emerging diseases research encompasses
many disciplines, and research advances that fall under the rubric of
emerging diseases will be relevant not only to specific diseases being
studied but to a broad range of disciplines such as vaccinology,
immunology, and drug development (Figure 5). In turn, research in these
areas is critical to advances in emerging and reemerging diseases. With a
sustained commitment to basic research and cross-sector collaboration,
important scientific findings and technological advances can be translated
into improved global health and reduced susceptibility to new microbial
threats.
[Fig]
Figure 5. Benefits of emerging diseases research.
Acknowledgment
The author thanks Greg Folkers for helpful discussion related to the
preparation of this manuscript.
References
1. Institute of Medicine, Board on International Health. America's vital
interest in global health. Washington: National Academy Press; 1997.
2. Centers for Disease Control and Prevention. Staphylococcus aureus with
reduced susceptibility to vancomycin–United States, 1997. MMWR Morb
Mortal Wkly Rep 1997;46:765-6.
3. Centers for Disease Control and Prevention. Update: isolation of avian
influenza A (H5N1) viruses from humans–Hong Kong, 1997-1998.
MMWR Morb
Mortal Wkly Rep 1998;26:1245-7.
4. The CVI strategic plan: managing opportunity and change: a vision of
vaccination for the 21st century. Geneva: Children's Vaccine
Initiative, 1997. Sponsored by UNICEF, United Nations Development
Program, World Health Organization, World Bank, Rockefeller
Foundation.
5. Two cheers for the multilateral malaria initiative. [editorial].
Nature 1997;388:211.
6. Fauci AS. Biomedical research in an era of unlimited aspi-rations and
limited resources. Lancet 1996;348:1002-3.
7. The Institute for Genomic Research. TIGR Microbial Database [database
online] [cited 1998 Apr 1]. Available from: URL: http://www.tigr.org.
8. World Health Organization. World Health Report 1997–conquering
suffering, enriching humanity. Geneva: The Organization; 1997.
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Health Policy Implications of Emerging Infections
Karen Hein
Institute of Medicine, National Academy of Sciences, Washington, D.C., USA
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The solutions to emerging disease problems involve politics and policy
issues, as well as solid science. The National Academy of Sciences'
Institute of Medicine (IOM), whose mission is to "improve the health of
people of the nation and the world," draws upon the expertise of elected
members as well as others in the United States and other nations to make
policy recommendations. Groups convene to debate contentious issues and
publish evidence-based reports with recommendations to government,
academia, industry, and the public.
Evidence-based reports are the foundation upon which policy can be built.
In this last decade, IOM has produced several documents that have focused
on emerging infections and provided a springboard for policy on a local,
nationwide, and international scale. The U.S. Capacity to Address Tropical
Infectious Disease Problems (1987) (1) concluded that U.S. capacity was
barely adequate and that improvement in policies and modest additional
funding could make a substantially stronger contribution to the field.
Required efforts included sustained support for basic and applied research;
accelerated development and testing of new preventive, therapeutic, and
diagnostic technologies; sustainable career structures for tropical disease
professionals; increased capacity to train U.S. tropical disease
professionals and those from developing countries in research and public
health service; development of disease surveillance capabilities;
strengthened institutional capabilities in developing countries; and
flexible, responsive administration of programs.
The Future of Public Health (1988) (2) report made three basic
recommendations regarding the mission of public health and defined its core
functions to be assessment, policy development, and assurance. It also
included guidance for the government's role in fulfilling the public health
mission and the responsibilities unique to each level of government. The
report has been a useful blueprint for the past decade.
Emerging Infections: Microbial Threats to Health in the United States
(1992)(3) identified significant emerging infectious diseases, determined
what might be done to deal with them, and recommended how similar future
threats might be confronted to lessen their impact on public health. The
document focused on factors contributing to disease emergence, not the
diseases themselves: human demographics and behavior, technology and
industry, economic development and land use, international travel and
commerce, microbial adaptation and change, and the breakdown of public
health measures.
Sexually Transmitted Diseases: The Hidden Epidemic (1997) (4) focused on
the need for a new social norm of healthy sexual behavior. The small
investment in prevention efforts was contrasted with the very high costs of
care for treating sexually transmitted diseases (STDs) (Figure 1). The
report also examined the obstacles and opportunities presented by managed
care. Limitations include the low priority for STD prevention, emphasis on
short-term cost savings, varying technical capabilities for diagnosis and
treatment, and patient concerns about confidentiality and treatment of
partners not enrolled in the same health plan. Lastly, opportunities for
training and continuing education in STD control and prevention are not
built into most managed care settings. The report called for several steps
including a national campaign to heighten awareness of the human and
financial costs of STDs and to promote the use of social marketing
techniques for their prevention. A recent innovative informational campaign
used a niche approach and a social marketing strategy with the spot video
Hittin' the Skins and the public service announcement Knockin' Boots (D.
Futterman, pers. comm.), geared toward alerting 16- to 21-year-olds of the
need for HIV testing.
[fig]
Figure 1. Estimated annual direct and indirect costs for selected sexually
transmitted diseases (STDs) and their complications in 1994 versus national
public investment in STD prevention and research in federal fiscal year
1994 (4).
Many related activities, in addition to the IOM reports, have underscored the
danger of emerging infectious diseases and reiterated the warnings about the
overall erosion of the U.S. public health system during the 1990s. The reports
also provided specific, detailed recommendations for action by individual
agencies. In 1994, the Centers for Disease Control and Prevention (CDC)
published Addressing Emerging Infectious Disease Threats: A Prevention
Strategy for the United States. In the same year, the U.S. National Science and
Technology Council's Committee on International Science, Engineering, and
Technology (an interagency working group) was convened to consider the
global threat of emerging and reemerging infectious diseases and in 1995
published the report Infectious Disease—A Global Health Threat. In 1995, the
National Security Council asked the federal government to examine its
preparedness to respond to global epidemics.
In 1995, the Food Safety and Inspection Service, CDC, and the Food and Drug
Administration (FDA) developed the Sentinel Site Study, which evolved into
FoodNet and now includes collection of more precise information on the
incidence of foodborne disease in the United States. In 1996, President
Clinton's administration set out a new policy to establish a worldwide
infectious disease surveillance and response system and expand certain
federal agency mandates to better protect American citizens.
In the 1996 NIAID Research Agenda for Emerging Infectious Diseases, the
National Institutes of Health described research and training issues
relevant to the national strategy for confronting the threat of emerging
and reemerging infections and related its approach to addressing these
issues.
In 1996, the Department of State established an Emerging Infectious
Diseases and HIV/AIDS Program to serve as a focal point for the development
and implementation of U.S. foreign policy objectives to improve the health
of U.S. citizens and to stem the spread of infectious diseases worldwide
through various international bilateral and multilateral negotiations. This
program has received $50 million in funding. Other government agencies,
including FDA, U.S. Agency for International Development, Department of
Defense, National Oceanic and Atmospheric Administration, National
Aeronautics and Space Administration, and U.S. Department of Agriculture,
have also examined the issue of U.S. vulnerability to epidemics and
resurgence of infectious disease threats.
The IOM's Forum on Emerging Infections is the most recent activity within
the National Academy of Sciences to keep sustained attention on these
issues. The forum was established in 1996 to provide a structured
opportunity for discussion and to scrutinize critical, and possibly
contentious, scientific and policy issues related to research on and the
prevention, detection, and management of new and reemerging infections. The
forum has organized a series of workshops to be conducted over 30 months.
Workshop topics include costs of infectious diseases, surveillance,
antimicrobial resistance, effects of health-care restructuring on public
health and basic research related to infectious diseases, capacity for
emergency response to emerging and reemerging infectious diseases,
education and training needs, predicting the future, and behavioral
interventions.
Orphans and Incentives (5), a 1998 report, is the first publication of the
forum; it focused on constraints that have left an undefined group of
"urgently needed medical products in an orphaned condition which demands
special attention." The authors examined these products across the product
cycle and then classified them into categories for which incentives might
be developed to bolster the competitiveness of such products in industrial
portfolios.
The 1998 report Antimicrobial Resistance (6), the second publication of the
forum, examined increases in the number of pathogens, multidrug-resistant
strains, compromised persons (including HIV-infected patients), deaths from
infection with resistant organisms, speed of the global spread, and costs
of health care. The report also examined decreases in the antimicrobial
armamentarium, amount of research and development expended when resistance
was not seen as a major threat, and funding for public health
infrastructure and addressed the following topics: expansion, coordination,
and improvement of the diverse elements of surveillance; need for
relatively small but thoughtful investments in research, clinical
management and practice, and policy; use of antibiotics in food production;
ways to prolong the effectiveness of existing antibiotics; basic research
and incentives for new antibiotics; and legal and regulatory mechanisms in
key areas of need.
A soon-to-be-published report on a March 1998 workshop on managed care will
examine the implications of managed care systems on emerging infections by
reviewing basic and clinical research, clinical practice guidelines,
surveillance and monitoring, prevention, education and outreach, and
product development.
These reports and events have examined research on emerging infectious
diseases and crafted a series of policy recommendations. They put forth a
rationale for why the United States should invest in global health. The
1997 report, entitled America's Vital Interest in Global Health (7),
provided a new framework for thinking about the benefits to the United
States, as well as to the rest of the world, of our increased
participation. The movement of two million people each day across national
borders and the growth of international commerce are inevitably associated
with transfers of health risks (e.g., infectious diseases, contaminated
food, terrorism, and legal or banned toxic substances). U.S. commitment to
global health serves to protect our people, enhance our economy, and
advance our international interests. Moreover, governments are no longer
the sole agents in the global health arena (Figure 2).
[fig]
Figure 2. The growing role of the World Bank in health (7).
The United States can contribute not only with funding, but also with the
scientific and technical expertise in its health sector. The United States should
lead from its strengths (medical science and technology) in the areas of research
and development, surveillance, education and training, global partnerships, and
coordination and leadership. In this way, the United States "can do well by doing
good."
Acknowledgments
The author thanks Carol Bock for her assistance in preparing this
manuscript and Jonathan Davis for collecting background materials.
References
1. The U.S. capacity to address tropical infectious disease problems.
Washington: National Academy Press; 1987. p. 88. Sponsored by the
Board on Science and Technology for International Development, Office
of International Affairs, National Research Council and Institute of
Medicine, National Academy of Sciences.
2. The future of public health. Washington: National Academy Press;
October 1988. p. 240. Sponsored by the Institute of Medicine, Division
of Health Care Services.
3. Lederberg J, Shope RE, Oaks SC Jr, editors. Emerging infections:
microbial threats to health in the United States. Washington: National
Academy Press; October 1992. p. 312. Sponsored by the Institute of
Medicine, Division of Health Sciences Policy and Division of
International Health.
4. Eng TR, Butler WT, editors. The hidden epidemic: confronting sexually
transmitted diseases. Washington: National Academy Press; 1997. p.
392. Sponsored by the Institute of Medicine, Board on Health Promotion
and Disease Prevention.
5. Harrison PF, Lederberg J, editors. Orphans and incentives: developing
technology to address emerging infections, Workshop Report.
Washington: National Academy Press; 1997. Sponsored by the Institute
of Medicine.
6. Antimicrobial resistance: issues and options. Workshop Report.
Washington: National Academy Press; 1998. Sponsored by the Institute
of Medicine, Forum on Emerging Infections.
7. America's vital interest in global health, protecting our people,
enhancing our economy, and advancing our international interests.
Washington: National Academy Press; 1997. Sponsored by the Institute
of Medicine, Board on International Health.
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Detection and Identification of Previously Unrecognized Microbial Pathogens
David A. Relman
Stanford University, Stanford, California, USA, and Veterans Affairs Palo
Alto Health Care System, Palo Alto, California, USA
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Features of a number of important but poorly explained human
clinical syndromes strongly indicate a microbial etiology. In
these syndromes, the failure of cultivation-dependent microbial
detection methods reveals our ignorance of microbial growth
requirements. Sequence-based molecular methods, however, offer
alternative approaches for microbial identification directly
from host specimens found in the setting of unexplained acute
illnesses, chronic inflammatory disease, and from anatomic
sites that contain commensal microflora. The rapid expansion of
genome sequence databases and advances in biotechnology present
opportunities and challenges: identification of consensus
sequences from which reliable, specific phylogenetic
information can be inferred for all taxonomic groups of
pathogens, broad-range pathogen identification on the basis of
virulence-associated gene families, and use of host gene
expression response profiles as specific signatures of
microbial infection.
For 100 years, efforts to detect and identify microorganisms have generally
begun with the inoculation and incubation of growth media in the
laboratory. Colony purification and preparation of limiting dilutions of
liquid culture media have provided at least two benefits: amplification of
microbial material and purification of single organisms along with their
direct descendants. Because some microorganisms are not particular in their
growth requirements, these efforts have yielded an array of diverse
microbial cultivation types. Serial propagation of microorganisms in the
presence of varied energy sources, analysis of their macromolecular
composition and their metabolic by-products, and use of specific
immunologic reagents have created a variety of systems for microbial
classification and identification. Some isolates purified from diseased
tissues of animal and human hosts produced identical disease when injected
into other, previously healthy hosts. By the latter half of the 20th
century, these findings had led to optimism about our ability to detect and
recognize microscopic life forms, particularly forms that can cause
disease.
Microbial cultivation methods opened up an unsuspected world of microscopic
life and presumed causative agents of human illness. However, much of this
world remained uncharacterized. In the external environment, certain
biochemical activities could best be explained by the presence of
microorganisms, although they could not be cultivated in vitro. Sergei
Winogradsky, a pioneering soil microbiologist of the early 20th century,
spoke about the "less docile" organisms that were not satisfied with
laboratory cultivation conditions. In the internal, privileged niches of
animals, microorganisms were sometimes visualized in diseased tissues, and
persons with typical clinical signs of infection would respond to
antibiotics, despite unsuccessful efforts at microbial propagation. That
conserved genomic sequences might be used to infer evolutionary ancestry
and be amplified directly from natural sites of infection provided the
framework for cultivation-independent approaches for microbial detection
and identification. In a few years, it became clear that most extant
microorganisms in the external environment had been completely overlooked
because of their resistance to cultivation on artificial media.
Sequence-Based Methods for Pathogen Discovery
What features of a genetic sequence make it useful for identifying
uncharacterized microorganisms? (1). First, the sequence should be
conserved among a relatively large number of known organisms. Second, its
rate of change should be constant over long periods and among diverse
organisms and should allow inferences of evolutionary distance among a wide
range of life forms; the sequence should not be subject to widely
discrepant degrees of evolutionary pressure. Third, the sequence should not
have been shared among different organisms by horizontal transmission.
Finally, the sequence should be amenable to broad-range amplification or
detection.
The sequence of the small subunit ribosomal RNA or DNA (ssu rDNA), among
other genomic sequences, meets these criteria. Ssu rRNA sequences were the
first to reveal a tripartite tree of cellular life, one that includes the
bacteria, archaea, and eukarya (2); few genetic sequences reliably reflect
the ancestry of such a wide array of cellular life as the ssu rRNA. Since
this realization nearly two decades ago, a large ssu rRNA sequence database
has accumulated (3), further enhancing the usefulness of this particular
locus. (More than 7,000 bacterial 16S rDNA sequences are now available).
Highly conserved regions of the ssu rDNA and ssu rRNA provide priming sites
for broad-range polymerase chain reaction (PCR) (or RT-PCR) and obviate the
need for specific information about a targeted microorganism before this
procedure. Thus, a previously uncharacterized bacterium, for example, can
be identified from an infected site or tissue by broad range bacterial 16S
rDNA amplification, sequencing, and phylogenetic analysis (4). This
approach was applied to the uncultivated bacteria of bacillary angiomatosis
in 1990 and of Whipple's disease soon thereafter (5,6). Because of the
usual presence of host DNA, eukaryotic pathogens (parasites, fungi) must be
approached either with domainwide primers and partially purified pathogens
or with range (e.g., kingdom)-restricted eukaryotic primers (7).
Broad-range PCR as a method for "pathogen discovery" is not limited to ssu
rDNA as a target or to cellular life. Any phylogenetically reliable family
of orthologous gene sequences found among a coherent group of
microorganisms can be targeted, as long as conserved priming sites can be
defined at sites that flank the informative region of sequence. For
example, a newly discovered hantavirus was identified as a cause of acute
pulmonary disease by using broad-range primers directed at a conserved
region of a coat protein-encoding genomic segment (8). A collection of
family-restricted broad-range primers is necessary to identify unrecognized
viral pathogens; this collection is not yet comprehensive.
Two other independent sequence-based methods are available for pathogen
discovery. One relies upon subtractive hybridization to isolate fragments
of nucleic acid that are unique (different) to one member of an otherwise
matched pair of specimens; these "difference" molecules are then
selectively amplified by using linker sequences that had been ligated to
all fragments derived from the infected specimen. Multiple rounds of
subtraction and amplification are required to find rare fragments within a
complex common background. Although better suited than differential display
or suppressive subtractive hybridization for low copy targets and highly
complex backgrounds (such as human genomic DNA), this method, known as
representational difference analysis (RDA) (9), is labor-intensive and
cumbersome. Nonetheless, it identified for the first time the presumed
causative agent of Kaposi sarcoma, human herpesvirus 8 (9). RDA enables
detection of any class of microorganism; however, it may be most useful for
DNA viruses. The third sequence-based pathogen discovery method takes
advantage of host immunologic recognition of an exogenous microbial agent.
Immune sera are used to screen an expression genomic library created from
an infected specimen. While laborious, this method has also uncovered an
important previously unrecognized pathogen for humans: hepatitis C virus
(10).
Sequence-based approaches take advantage of the speed and sensitivity of
rapidly evolving molecular biologic methods and the specificity of
genotypic characterization. Consensus PCR has the additional advantage of
being able to target families of sequences preselected for their
reliability in the inference of evolutionary relationships. However, all
approaches have limitations. One of the most important for sequence-based
methods involves the processing of clinical specimens. Difficulties include
heterogeneity of sample, wide variation in the numbers of microbial targets
in any given sample, resistance of some microorganisms to digestion and
subsequent release of nucleic acid, and presence of PCR inhibitors in
varying amounts and typesnot to mention ubiquitous microbial nucleic acid
contamination of PCR reagents, specimen collection materials, and
externally exposed surfaces of the host. These problems reflect the
intrinsic biologic variability of a highly complex, partially characterized
host. Standardized procedures that produce consistent results with large
numbers of clinical specimens are rare. Despite increasing attention to
these issues, particularly in the private and commercial sectors, resource
commitment and technology advances have lagged behind the development of
methods for sequence acquisition and analysis. In fact, it is far easier to
generate a putative microbial sequence from a clinical specimen than it is
to understand its clinical relevance.
As the process of pathogen discovery and detection turns to the fundamental
signature macromolecules of all life forms and away from reliance on
cultivation, we increasingly rely on our ability to understand a putative
microorganism from its genetic sequence. Many families of
virulence-associated genes and gene products are recognizable from their
sequence, and their targets are predictable. To predict whether the
microorganism whose presence is inferred from amplified genomic fragments
is the cause of the disease under study, however, is far more problematic.
A replicating organism with which to observe behavior (e.g., drug
resistance) and reproduce disease is not available. In fact, the viability
of the putative microorganism may not be certain. Although detection of
different molecular markers (e.g., specific mRNAs, rRNA/rDNA ratio,
resistance-encoding loci) might help resolve some of these questions, it is
difficult to determine whether these genotypes and markers all derive from
the same organism in that clinical specimen. From a practical standpoint,
proof of disease causation from sequence-based investigations will require
data that address strength and specificity of association, target dosage
effects, temporal considerations, response to therapy, and use of in situ
hybridization (11). The selection of proper experimental and control
specimens is paramount.
Settings for Pathogen Discovery
Explorations of microbial diversity within the external environment have
yielded surprising results. Nearly all bacteria and archaea revealed by
broad-range sequence "mining" in fresh water sites, oceans, surface soils,
and deep geologic niches had not been recognized or ever cultivated in the
laboratory. Novel kingdoms of life have been discovered with these
genotypic methods (12,13). It has been estimated that only 0.4% of all
extant bacterial species have been identified. Does this remarkable lack of
knowledge pertain to the subset of microorganisms both capable and
accomplished in causing human disease? The molecular methods described
above could be applied in several settings in which one might expect to
find uncharacterized microbial pathogens.
Acute, Life-Threatening Unexplained Illness
All clinicians are aware of cases characterized by sudden onset of fever,
flu-like syndrome, and hemodynamic instability, often accompanied by
leukocytosis or leukopenia and rapid deterioration of one or more organ
systems. In some cases, despite the strong suggestion of a microbial
etiology, conventional diagnostic methods cannot determine the cause. The
dramatic nature of these illnesses belies their potential importance to
public health and their value in revealing "emerging" agents of disease. An
Unexplained Deaths and Critical Illnesses Project has been designed to
identify and characterize these illnesses (14). Laboratory investigations
include the application of broad-range ssu rDNA PCR. RDA is planned for
carefully selected cases with matched control samples. Appropriate
specimens have been obtained in only a minority of cases, but positive
results from cerebrospinal fluid samples are encouraging. Two lessons have
been learned. 1) Well-recognized pathogens may be the cause of some
critical illnesses that cannot be explained with traditional diagnostic
methods. 2) The process of clinical specimen selection and collection may
need to be rethought jointly by molecular biologists and clinicians.
Chronic Idiopathic Disease
Adaptation and cooptation, features that favor long-term survival of both
participants, dominate most host-pathogen relationships. Persistent or
intermittent inflammation indicates host perturbation and a subtle
imbalance to the relationship and gives rise to clinical manifestations. In
fact, the epidemiologic, clinical, and pathologic features of many chronic
inflammatory diseases are consistent with a microbial cause, but intimate
or symbiotic host-pathogen relationships are among the most difficult to
decipher and mimic in the laboratory. Thus, it is not surprising that
although microbial etiologies are attractive hypotheses for many chronic
diseases, culture-dependent methods have not produced much evidence.
Serologic approaches have been useful in providing some leads. For example,
the first clues of a possible chlamydial etiology for coronary
atherosclerosis were serologic findings. Corroborating data then became
available from the use of molecular and in situ methods.
The list of chronic inflammatory diseases with possible microbial
etiologies is extensive (15); it includes sarcoidosis, various forms of
inflammatory bowel disease, rheumatoid arthritis, systemic lupus
erythematosus, Wegener granulomatosis, diabetes mellitus, primary biliary
cirrhosis, tropical sprue, and Kawasaki disease. In this discussion, the
concept of pathogenic mechanism should be viewed broadly. Many chronic
diseases may result from damage or disruption of local immunologic
surveillance systems by microbial infection or products; the microorganism
is subsequently cleared away, but autoimmune responses or responses
directed against commensal flora persist. By the time typical pathologic
and clinical findings are produced and the disease is recognized, the
inciting agent or its nucleic acids may be gone. Under these circumstances,
the optimal time for specimen collection may be well before the disease
takes on its characteristic features. Clinical suspicion, astute
observation, and identification of disease-predisposing factors are
critical. Surprisingly few published studies describe the application of
broad-range molecular pathogen discovery methods to the diseases listed
above or to other enigmatic chronic disease syndromes. With the finding of
microbial sequences in these disease settings, experimental criteria for
identifying disease causation must be rigorously pursued (11).
Commensal Microbial Flora
The human body harbors a 10-fold greater number of microbial cells than
human cells. The commensal flora includes microorganisms that occasionally
cause disease, especially when host defenses are impaired (due to
immunosuppressive drugs, disruption of anatomic barriers, suppression of
bacterial flora with antibiotics, or insertion of artificial surfaces).
However, in many hosts with impaired conditions and signs and symptoms of
infectious disease, an etiologic agent is not identified. If our
understanding of microbial diversity within the human-associated commensal
flora is as limited as it was of external environments, these clinical
observations may not be surprising. That is, the inability to cultivate
some of the commensal flora may explain the failure to diagnose related
disease. In addition to revolutionizing environmental microbiology,
molecular methods may offer rewards for clinical microbiology and the study
of internal environmental niches.
Recent research has compared culture-dependent and culture-independent
methods of characterizing human commensal flora (16-19). The results
suggest that members of at least some phylogenetic groups, e.g., the
spirochetes, have been ignored by traditional approaches. Direct
comparisons of these two methods will likely show biases and deficiencies
with each; nonetheless, important aspects of microbial diversity will be
revealed by one and not the other. A complete enumeration of complex
microbial communities is not the primary goal. Key members play crucial
roles in maintaining the health of the ecosystem (20,21), and understanding
community interactions and function may be the more important goal.
Arthropod Vectors and Small Animal Reservoirs
Several prominent, recently described cultivation-resistant pathogens are
transmitted to humans from small animal reservoirs through airborne or
vector-borne routes. These pathogens include borreliae (22), bartonellae
(23), ehrlichiae, rickettsiae, babesiae, and hantaviruses. These reservoirs
and the relevant vectors are attractive targets for pathogen discovery.
Searches for restricted groups of microorganisms, searches within
restricted host anatomic niches, or searches that include subtractive or
differential techniques may be warranted, since all these targets are also
hosts for their own commensal (e.g., intestinal) flora. Microorganisms that
use arthropod vectors often express different sets of genes within vector
versus animal host (e.g., human). Human immune recognition of
differentially expressed gene products might help distinguish
vector-associated pathogens from nonpathogenic vector-associated flora.
Phylogenetic Diversity of Microbial Pathogens
Nearly all kingdoms within the domain Bacteria contain recognized human
pathogens (Figure). Of those bacterial pathogens identified only by molecular
methods, many are clustered within some kingdoms and divisions, such as the
alpha-proteobacteria, which include many organisms that form endosymbiotic
relationships with their hosts.
[Fig]
Figure. Evolutionary tree of the domain Bacteria based upon comparative
analysis of nearly complete 16S rDNA sequences.
Nearly all humans harbor in the intestinal tract Archaea, among the most
diverse and numerous cellular life forms on earth (24), most notably
methanogens. So why are there no known archaeal pathogens? Although some of
the most well-known archaea were first identified in (and were assumed to
require) extreme environments, they are also found in environments similar
to those found within the human body. However, in vitro cultivation methods
for many archaea are unavailable, so how would we know if archaeal
pathogens existed? Molecular reagents for archaeal detection and
identification, i.e., rDNA-based primers and probes, have not been
systematically applied to human disease-associated specimens. Without such
analyses, finding these organisms in clinical samples would be unlikely.
Genomics and Newer Technologies
The ultimate genotype of a microorganism is its complete genome sequence.
Approximately 15 microbial genomes have been sequenced in their entirety,
and the rapid evolution of and large-scale investment in DNA sequencing
technology predict full genome sequencing of approximately 50
microorganisms by the year 2000. This massive infusion of primary sequence
data unleashes the potential to identify new families of broadly conserved
orthologous genes that could be used to infer accurate phylogenies at every
level and sector of the evolutionary tree. The number of completed genome
sequences is too small to effect this goal (25). The sequence data sets for
newly characterized genes are too small to assess the reliability of the
phylogenies they predict. The problem imposed by horizontal gene transfer
is now more apparent with the analysis of multitudes of gene families. To
identify a well-characterized microorganism, an exact genotypic "hit" with
a highly variable locus is sufficient. Likewise, clonality and clone
identification can be determined with sequences from collections of
polymorphic, but conserved loci, e.g., "housekeeping genes" (26). But for
an unrecognized organism, the sequence locus or loci selected for
genotyping must be highly conserved and phylogenetically informative and
reliable. Over the next 5 years, with the increasing use of large-scale
comparative genomic techniques, microbial sequence databases will represent
the broad diversity among distant ancestral relatives, as well as the fine
differences among closely related cousins. Assessment of putative universal
sequences can be undertaken. All these developments and future trends apply
equally well to the wide array of animal viruses and viral genomes (Table
1). As genotypes become more easily interpreted, they will continue to
displace phenotypic characterization as the basis for pathogen recognition.
Table 1. Newer diagnostic technologies
----------------------------------------
1. High-density DNA microarrays
* broad-based pathogen detection and genes.
characterization: bacteria,
eukarya, viruses
* virulence-associated gene families
* comprehensive host gene expression
profiles
2. Improved nucleic acid subtractive
methods
3. Novel bioassays for toxin activity
* neurons–or myocytes–on-a-chip
----------------------------------------
Often the only difference between a pathogenic and a nonpathogenic strain of the
same species, e.g., enteropathogenic and nonenteropathogenic Escherichia coli, is
a small set of virulence These differences are not reflected in the ancestry inferred
from more stable chromosomal markers (Table 2). Yet detection of these genes is
a fundamental aspect of pathogen identification. Microbial virulence is a
phenotype whose genetic basis is rapidly being revealed. Families of
virulence-associated genes responsible for microbial adherence, toxicity,
specialized secretion, environmental sensing, and subversion of immune defenses
have been defined, albeit with many sequence variations on a theme (27,28). One
of the most important features of these genes is their proclivity toward horizontal
transfer and over relatively rapid time scales. Genome sequencing efforts have
facilitated, and will continue to facilitate, this approach to pathogen discovery.
Physical clusters (or islands) of virulence genes are being identified, and their
distinctive composition and boundaries are being defined (29). One might well
imagine the development of a comprehensive set of consensus primers and probes
for detecting these gene families, clusters, and islands (Table 1).
Table 2. Pathogens that may be difficult
to detect or identify
----------------------------------------
1. Pathogens that establish intimate
relationships with the host
* endosymbionts and intracellular
organisms
2. Chimeras: natural versus man-made?
3. "Nonpathogens" that acquire
virulence-associated genes
4. Microorganisms without "universal"
sequences?
----------------------------------------
With increasing value placed on genotypic information and increasing
numbers of potentially useful genotyping loci, the technology of sequence
determination and primary genomic characterization has assumed center
stage. Goals include speed, convenience, and large-scale sequencing. High
density DNA microarray technology is one of the most promising in this
context (Table 1). Depending on the format, microarrays can be used to
detect nucleic acid polymorphisms or to sequence de novo; they can also
quantitate mRNA. At least two basic applications of DNA microarray
technology are available for pathogen detection and identification; neither
has been fully developed or tested clinically (Table 1). The first would
consist of a set of probes designed to assess ssu rDNA sequence diversity
of all known monophyletic groups of bacteria, archaea, viruses, and
nonanimal eukarya. Other phylogenetically reliable loci might be
substituted for rDNA or included as well. In addition, consensus probes for
families of virulence-associated genes, as described above, would
facilitate identification of unsuspected or newly acquired pathogenic
attributes in organisms not usually associated with these traits.
Differential hybridizations and multiple fluorophores allow easy detection
of hybridized target and normalization of quantified values to a reference
sample. This sort of broad-range "pathogen detection chip" would identify
mixed infections, as well as chimeric or novel microorganisms (Table 2); it
could rapidly create an inventory of highly complex microbial communities
and measure changes in individual members as a function of varying
environmental conditions.
The second theoretical use of DNA microarray technology for pathogen detection
would focus on host gene responses. Arrays in current use at academic and
commercial research laboratories are capable of quantitating expression responses
by 10,000 to 20,000 human genes simultaneously (30-34). During most infectious
diseases, directly affected tissues, secondary sites, and circulating leukocytes will
likely display sets of common nonspecific expression responses; however, since
each microbial pathogen interacts with and manipulates the host in a complex and
unique manner, within these highly complex patterns there will also likely be
critical diagnostic signatures that distinguish infection by one pathogen from
infection by another. Furthermore, these stereotypic expression patterns will
evolve. The time of initial host exposure to a pathogen might be determined by
comparing new expression patterns with a suitable preexisting set of timed
profiles. Patterns will provide clues about the pathogenesis of chronic
inflammatory disease (35). Through the identification of key response genes
might emerge novel diagnostic assays for their putative protein products and
novel strategies for interfering with or blocking disease pathogenesis.
In many cases, infection-associated tissue damage occurs in the absence of
intact microorganisms. Toxin-mediated disease is a prominent example.
Often, microbial toxins act at a distance from the original site of
microbial toxin production and release. In this setting, genotypic
approaches for microbial detection may not be appropriate; in addition to
the assessment of host responses, novel bioassays for toxin activity are
attractive options (Table 1). For example, in a system designed by Greg
Kovacs at Stanford University, neurons or myocytes are cultivated on the
electrical contacts of a miniaturized circuit board. The electrical output
and properties of these cells can be monitored and analyzed as they are
exposed to diverse membrane-active toxins. Although this technology is at
an early stage of development, we know that such cells are extremely
sensitive to chemical toxins, and this sensitivity can be recorded in the
form of altered action potentials and changes in impedance and cell
movement. Experiments are under way to test cell responses to biologic
toxins in a variety of clinically relevant experimental conditions.
Relationships between Pathogen and Host
As more sensitive and comprehensive methods for uncovering human-associated
pathogenic microorganisms identify previously unsuspected host-pathogen
relationships, the nature of these relationships may need to be rethought (36,37).
Parasitism and commensalism are probably not the complete story; mutualism
may be more common in the human host than is usually taught. Evidence of
coevolution between host and microbe suggests codependence. The endosymbiont
theory for the origin of eukaryotic organelles is consistent with the same (38).
Microbial remnants and cryptic genomic fragments may not be so uncommon
within the human genome; for example, approximately 1% of the human genome
is retrovirus sequence (39). Some of these viral genes may be expressed during
local inflammation. The real challenges in pathogen discovery will be the
problems of sequence interpretation, clinical relevance, and proof of causation. In
the end, pathogen discovery will by necessity be a multidisciplinary effort (40).
Only with the coordinated interaction of epidemiologists, pathologists, and
clinicians will the role of microorganisms in disease be clearly defined.
[photo1]
[photo2]
David A. Relman is assistant professor of medicine and of
microbiology and immunology at Stanford University, Stanford, California;
he is also staff physician at Veterans Affairs Palo Alto Health Care
System, Palo Alto, California. His research interests include Bordetella
pathogenesis, molecular and genomic aspects of pathogen recognition by the
host, and development and application of molecular methods for the
identification of unrecognized microbial pathogens.
References
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2. Woese CR, Kandler O, Wheelis ML. Towards a natural system of
organisms: proposal for the domains Archaea, Bacteria, and Eucarya.
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The Emergence of Bovine Spongiform Encephalopathy and Related Diseases
Sir John Pattison
Medical School of University College London, London, United Kingdom
---------------------------------------------------------------------------
Since 1986, approximately 170,000 cases of bovine spongiform
encephalopathy (BSE) have occurred among approximately one
million animals infected by contaminated feed in the United
Kingdom. A ruminant feed ban in 1988 resulted in the rapid
decline of the epidemic. Transmissible spongiform
encephalopathies due to agents indistinguishable from BSE have
appeared in small numbers of exotic zoo animals; a small
outbreak among domestic cats is declining. Creutzfeldt-Jakob
disease (CJD) has been intensively monitored since 1990 because
of the risk BSE could pose to public health. In 1995, two
adolescents in the United Kingdom died of CJD, and through the
early part of 1996, other relatively young people had cases of
what became known as new variant CJD, whose transmissible agent
(indistinguishable from that of BSE) is responsible for 26
cases in the United Kingdom and one in France. Areas of concern
include how many cases will appear in the future and whether or
not use of human blood and blood products may cause a second
cycle of human infections.
Before the 1980s, a number of diseases of animals (scrapie, chronic wasting
disease, and transmissible mink encephalopathy) and humans
(Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, and
kuru), in spite of distinctive individual features, could be unified by the
term transmissible spongiform encephalopathies (TSEs). In 1986, bovine
spongiform encephalopathy (BSE) was first identified in indigenous cattle
in the United Kingdom (1). A variety of clinical signs have been observed,
but the three cardinal features of the disease are nervousness, heightened
reactivity to external stimuli, and difficult movement, particularly of the
hind limbs (2). Spongiform change is evident in the brain (1), and
neuropathologic tests remain the mainstay of a BSE diagnosis. The disease
was transmitted experimentally to mice (3) and cattle (4) by use of brain
homogenates from cattle with clinical BSE; thus BSE has all the features
that define classical TSEs.
The BSE Epidemic
Some 1985 cases were diagnosed retrospectively; other cases occurring
before 1986 probably went unnoticed. Since BSE was recognized, more than
170,000 cases were reported in the United Kingdom through the end of 1997.
The epidemic curve, which peaked in 1992, is now in rapid decline (Table
1). Approximately two thirds of the dairy herds in the United Kingdom have
had at least one case of BSE compared with only one sixth of the beef
suckler herds. Furthermore, most of the affected suckler herds contained
animals originating from dairy herds, which are fed differently.
Table 1. Annual incidence of
bovine spongiform encephalo-
pathy in the United Kingdom,
1985-1997
--------------------------------
Year Number of cases
------------------------------------
1985 14
1986 60
1987 630
1988 2,184
1989 7,137
1990 14,181
1991 25,032
1992 36,682
1993 34,370
1994 23,945
1995 14,300
1996 8,016
1997 4,052
--------------------------------------
Shortly after the recognition of BSE, epidemiologic studies indicated that the
source of infection was the meat and bone meal used in concentrated cattle feed
(5). Subsequently, in July 1988, ruminant protein in ruminant feed was banned.
This ban immediately reduced the incidence of new infections, which began to
be reflected in a diminution in the incidence of clinical cases 5 years later (the
average incubation period) in 1993. Nevertheless, almost 36,000 cattle with BSE
were born after the ruminant feed ban (a few as late as 1994), which indicates
that the ban was not completely effective. Ruminant protein could be included in
pig and poultry feed, and cross-contamination of cattle feed in the production
mills and perhaps accidental exposure of cattle on the farm were possible until
the feeding of mammalian protein to all farm animal species in the United
Kingdom was prohibited in 1996.
The average age at which clinical BSE manifests itself is 4 to 5 years (6). Many
animals in the national U.K. herd are slaughtered at significantly younger ages,
and those infected with BSE would not have had a chance to develop the
disease. Using methods developed for the retrospective analysis of the AIDS
epidemic, Anderson and colleagues (7) calculated that approximately one
million animals in the U.K. herd must have been infected to have produced
170,000 clinical cases of BSE. These same workers predicted the number of
cases of BSE that would occur in 1996 and in subsequent years (Table 2). The
calculations are based on a dominant feedborne source of infection; a small
amount of cow-to-calf transmission was included because a long-term study,
conducted by the U.K. Ministry of Agriculture, Fisheries and Food, indicated an
increased incidence of BSE in calves born to mothers in the late stages of the
incubation period of the disease (8). The results are compatible with a
cow-to-calf transmission of approximately 10%, which in itself is not sufficient
to perpetuate the BSE epidemic. The calculations predict a small number of
cases and very few new infections by the beginning of the next decade. The
predictions have been validated by the actual numbers in 1996 and 1997, which
were 8,016 and 4,149, respectively (9).
Table 2. Predictions of new infections and cases
of BSE(sup a) from 1996-2001(sup b)
---------------------------------------------------------------
New Infections Cases
-------------------------------------------------------
95% 95%
Expected Prediction Expected Prediction
Year value interval value interval
---------------------------------------------------------------
1996 189 (155-11,300) 7,386 (6,541-8,856)
1997 95 (63-236) 4,111 (3,006-7,664)
1998 38 (21-214) 1,864 (1,153-7,052)
1999 12 (5-162) 682 (388-5,909)
2000 3 (1-86) 221 (128-3,660)
2001 1 (0-33) 72 (45-1,592)
----------------------------------------------------------------
(sup a)Bovine spongiform encephalopathy.
(sup b)Information extracted from (7).
Infection in Other Animals
BSE has also been transmitted to exotic ruminants in zoos in the United
Kingdom. Between 1986 and 1992, cases have occurred in bison, nyala,
gemsbok, two species of oryx, greater kudu, and eland. These animals became
infected by eating the same meat and bone meal-containing concentrated feed
responsible for the disease in cattle. BSE infection in species other than
ruminants was always considered possible. Careful watch was kept on the
packs of hounds used for hunting in the United Kingdom because they are often
fed carcasses unfit for human consumption. Spongiform encephalopathy has not
occurred in dogs; however, in 1990, a case of spongiform encephalopathy was
diagnosed in domestic cats; 81 additional cases in cats have occurred with a
wide geographic spread throughout the United Kingdom. The true incidence is
probably many times higher than observed because diagnosis is patchy and the
disease was not statutorily notifiable until 1994. The annual incidence at the
height of the outbreak was probably 10 to 15 cases per million cats (Wilesmith,
pers. comm.). The most likely source of the infection was commercially
produced cat food. In 1989, the pet food industry removed the dangerous bovine
tissues, the specified bovine offal, before a statutory ban in 1990. The number of
cases of feline spongiform encephalopathy (FSE) diagnosed in the United
Kingdom has been declining since 1994 (1994, 16 cases; 1995, 6 cases; 1997, 6
cases) (Table 3). Only one cat, an adopted stray, was apparently born after the
ban on specified bovine offal in pet food. A TSE indistinguishable from BSE
has also been found in puma, cheetah, ocelot, and a tiger in zoos in the United
Kingdom between 1992 and 1995. These animals became infected as a result of
being fed raw meat, which would have included bovine central nervous system,
a practice which has now ceased.
Table 3. Number of cases of
feline spongiform
encephalopathy in the United
Kingdom by year of diagnosis
(MAFF, personal communication)
-----------------------------------------------
Year Number of cases
-----------------------------------------------
1990 12
1991 12
1992 10
1993 11
1994 16
1995 8
1996 6
1997 6
1998(sup a) 4
------------------------------------------------
(sup a)= To May 1, 1998
Human Disease and BSE
Control Measures
The risk to human health from BSE was always recognized. The principal
protective measure was the November 1989 ban on the use of certain specified
bovine offal in human food. As with scraple, the tissues banned were those
likely to contain the highest concentrations of the transmissible agent (brain,
spinal cord, tonsil, spleen, thymus, and intestine of cattle older than 6 months of
age). The intestine and thymus of calves was added to the list in 1994 when a
long-term pathogenesis study in cattle by the Ministry of Agriculture, Fisheries
and Food indicated that the transmissible agent could be found in the terminal
ileum (it is assumed that the agent was present in Peyer's patches). In 1996 the
whole head, other than the tongue, was formally banned because of concern
about possible contamination with brain. Since the banned tissues now contain
more than offal, the tissues are referred to as specified bovine material. During
1995, it became clear that spinal cord was not being completely removed from a
small number of carcasses that were subsequently certified as fit for human
consumption. Consequently, in December 1995 the U.K. government banned the
use of bovine vertebral column for the production of mechanically recovered
meat. In March 1996, when it became clear that human disease related to BSE
was "probable" rather than "theoretical," the U.K. government introduced the
over-30-month scheme, which allowed only animals under the age of 30 months
to be used for human food, provided that all the banned specified bovine
material had been removed. This added an extra margin of safety because cattle
can be reasonably accurately aged by their dentition at 30 months and because
BSE is relatively rare under the age of 30 months. Only 265 cases occurred in
cattle younger than 30 months, and during 1997, the youngest animal with BSE
was 37 months of age (Ministry of Agriculture, Fisheries and Food, pers.
comm.). In the second half of 1997, the long-term pathogenesis experiment
indicated that the transmissible agent of BSE could be recovered from the dorsal
root ganglia of experimentally infected animals toward the end of the incubation
period. Also, in one animal the agent was transmitted by intracerebral
inoculation of mice with bovine bone marrow. Accordingly, in December 1997
the U.K. government introduced legislation to ban the sale of beef on the bone,
even from animals under 30 months of age. Many in the United Kingdom
thought that this regulation to prevent an extremely small risk of transmitting
BSE in T-bone steaks and rib of beef was unnecessary. Nevertheless, the
introduction of the specified bovine offal ban in 1989 and its subsequent
refinements have ensured the safety of beef and beef products that now enter the
human food chain in the United Kingdom. Even so, as a consequence of the
emergence of new variant CJD, a worldwide ban on the sale of U.K. beef and
beef products was introduced by the European Union in March 1996 and is still
in force with the exception of a recent (March 1998) relaxation for certain herds
in Northern Ireland.
New Variant CJD
Clearly, the first measures to protect human health were introduced before
any human disease could be related to BSE. To guard against the possible
emergence of such disease (or diseases), the U.K. Department of Health set
up a CJD Surveillance Unit in 1990. The purpose of the unit was to monitor
the trends in incidence of CJD and any unusual features among cases.
Concern was first focused on the 1995 cases of the third and fourth U.K.
farmer since 1990 to be confirmed as having CJD. Statistically, the chances
of four such cases occurring in 6 years in the United Kingdom were very
small. However, the clinical features of the disease were typical of
classical CJD, and collaboration between the CJD Surveillance Unit and
other European countries indicated that farmers were overrepresented
compared with CJD cases in countries with no BSE. Subsequently, classic CJD
was confirmed in these farmers; no further cases have been diagnosed in
U.K. farmers, and the significance of the high incidence in 1995 is
diminishing.
The death in May 1995 of the first adolescent ever to be diagnosed with CJD
in the United Kingdom was followed in October 1995 by the death of a second
adolescent; by January 1996, three other young (29 years of age) persons
became ill. Atypical pathologic results were beginning to be defined in
these patients; and on March 8, 1996, eight cases of what came to be known
as new variant CJD or variant CJD (vCJD) were reported to the Spongiform
Encephalopathy Advisory Committee. The cases were distinguished by the
relatively young age at which the symptoms started (10,11). That age range
is now 16 years to 52 years. The duration of the illness is relatively
long, averaging approximately 14 months as opposed to the 4 to 5 months in
classic CJD. The early symptoms are often psychiatric, and it may be 6 or 7
months before any neurologic signs appear. The characteristic
electroencephalogram pattern of sporadic CJD is not seen in vCJD, and
pathologic results show florid plaques and extensive cerebellar involvement
with multiple PrP deposits. As with BSE and FSE, the neuropathologic
appearances are the mainstay of laboratory confirmation. Magnetic resonance
imaging scanning and detection of 14-3-3 protein can be helpful. Early
evidence indicates that the diagnosis can often be made from tonsil
biopsies (12). Otherwise, diagnosis must depend upon brain biopsy or
postmortem examination.
When on March 20, 1996, the U.K. government announced the existence of 10
cases of vCJD and the opinion of the Spongiform Encephalopathy Advisory
Committee that these were probably related to BSE, three questions
immediately arose. The first was, "Is there really any link with BSE?"
Additional evidence emerged from the work of Collinge and his colleagues
(13) on the analysis of the PrP fragments after protease digestion. The
position of the three fragments and the relatively high concentrations of
the di-glycosylated form indicated that vCJD was distinct from the
previously recognized forms of CJD and that similarities existed between
the cases of vCJD and BSE and FSE. In 1997, the first results were
published from the classic strain typing experiments initiated during 1996
(14). The characteristics of material from cases of vCJD, in terms of
incubation period and lesion profile in RIII mice, were identical to those
from cases of BSE and FSE. These observations are confirmed now in C57
black mice. Thus, vCJD can now be regarded as human BSE in the same way
that FSE is regarded as feline BSE. The second question was, "What is the
route of transmission from cattle to humans?" So far we have no evidence,
only a working hypothesis, that transmission was likely from inclusion in
the human food chain of tissues that contain the highest concentration of
the transmissible agent. The major differences in human exposure to these
tissues would have occurred first when sick animals were banned from the
human food chain in 1988 and again in 1989 when the specified bovine offals
of otherwise healthy animals were removed from the human food chain.
Studies continue in an attempt to answer the third question, "How many vCJD
cases will there be in the future?" So far, 26 cases have been diagnosed in
the United Kingdom (Table 4) and 1 in France. Incidence has not increased
since vCJD was first diagnosed in 1995. If instead of looking at the date
of death one looks at the date of onset of the symptoms in the 26 patients,
two new cases occurred on average every quarter since 1994. All cases have
been methionine homozygotes at codon 129 of the PrP gene. In the general
population approximately 40% have such a genotype; 10% are valine
homozygotes, and 50% are heterozygotes. An analysis of classic sporadic CJD
indicates that 80% of those cases are methionine homozygotes, 10% valine
homozygotes, and 10% heterozygotes. It is perhaps not surprising,
therefore, that the first cases of vCJD to be seen are methionine
homozygotes.
Table 4. Creutzfeldt-Jakob disease in the United Kingdom
---------------------------------------------------------------------
Deaths of definite and probable cases
--------------------------------------
Year Refer- Spora- Iatro- Fami- GSS(sup a) nvCJD(sup b) Total
rals dic genic lial
-----------------------------------------------------------------------
1994 116 52 1 3 3 0 59
1995 86 34 4 2 3 3 46
1996 133 40 4 2 4 10 60
1997 152 42 6 3 0 10 61
1998(sup c) 35 3 0 1 0 2 6
-----------------------------------------------------------------------
(sup a)Gerstmann-Straussler-Scheinker syndrome.
(sup b)New variant Creutzfeldt-Jakob disease.
(sup c)To Apr 30, 1998. Figures released by U.K.
Department of Health June 1, 1998.
Only one published analysis has predicted the number of future nvCJD cases
after constraining the models used to the known and surmised facts at the time
(15). The total number of future cases will depend critically on the average
incubation period of vCJD. At present, we have no way of determining that;
therefore, it remains too early to predict with any accuracy the total number of
future cases. It remains possible that the outbreak of vCJD cannot be regarded as
a single curve and that the small number of cases have occurred in persons who
are extremely susceptible for unknown reasons.
The Future
Much has happened already as a consequence of the emergence of BSE in U.K.
cattle. The appropriate measures are in place to protect public health and
end the BSE epidemic in cattle and other affected species. These measures
are more rigorously enforced than ever before. It is difficult to see what
could be done to make the BSE epidemic decline more rapidly than it already
has, short of slaughtering the entire U.K. herd, which would be unnecessary
and impractical. From now the question is likely to be how to withdraw some
of the restrictions on U.K. beef and beef products. The exemptions are
likely to be herd based (as is the case with Northern Ireland) or date
based after the total ban on the use of meat and bone meal in the feed of
any farm animals in the United Kingdom in 1996. In terms of the protection
of public health, all the necessary measures are in place. Two further
concerns remain and are actively under consideration: whether or not BSE
exists in the sheep flocks and whether the cases of vCJD in the United
Kingdom will be sufficient to generate concern about a second wave of
transmission within the human population as a consequence of the use of
blood and blood products. With respect to the former, the detection of
sheep with scrapie-like diseases in the United Kingdom and the typing of
strains from affected animals are being intensified. With respect to blood
and blood products, some restrictions on the use of U.K. raw materials for
the production of blood products are already in place, and a detailed risk
assessment in relation to blood transfusion is awaited.
Sir John Pattison is a virologist and dean of the Medical School,
University College London, and Chair, U.K. Spongiform Encephalopathy
Advisory Committee.
References
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2. Wilesmith JW, Hoinville LJ, Ryan JBM, Sayers AR. Bovine spongiform
encephalopathy: aspects of the clinical picture and analyses of
possible changes. Vet Rec 1992;130:197-201.
3. Fraser H, McConnell I, Wells GAH, Dawson M. Transmission of bovine
spongiform encephalopathy to mice. Vet Rec 1988;123:472.
4. Dawson M, Wells GAH, Parker BNJ. Preliminary evi-dence of the
experimental transmissibility of bovine spon-giform encephalopathy to
cattle. Vet Rec 1990;126:112-3.
5. Wilesmith JW, Wells GAH, Cranwell MP, Ryan JBM. Bovine spongiform
encephalopathy: epidemiological studies. Vet Rec 1988;123:638-44.
6. Stekel DJ, Nowak MA, Southwood TRE. Prediction of future BSE spread.
Nature 1996;381:119.
7. Anderson RM, Donnelly CA, Ferguson NM, Woolhouse MEJ, Watt CJ, Udy
HJ, et al. Transmission dynamics and epidemiology of BSE in British
cattle. Nature 1996;382:779-88.
8. Donnelly CA, Ghani AC, Ferguson NM, Wilesmith JW, Anderson RM.
Analysis of the bovine spongiform encephalopathy study: evidence for
direct maternal transmission. Appl Statist 1997;43:321-44.
9. Lawson C, Herd L, editors. BSE Enforcement Bulletin 1998. Ministry of
Agriculture, Fisheries and Food; Bull. No. 20; p. 2.
10. Will RG, Ironside JW, Zeidler SN, Cousens SN, Estibeiro K, Alperovitch
A, et al. A new variant of Creutzfeldt-Jakob disease in the UK. Lancet
1996;347:921-5.
11. Zeidler M, Stewart GE, Barraclough CR, Bateman DE, Bates D, Burn DJ,
et al. New variant Creutzfeldt-Jakob disease: neurological features
and diagnostic tests. Lancet 1997;350:903-7.
12. Hill AF, Zeidler M, Ironside J, Collinge J. Diagnosis of new variant
Creutzfeldt-Jakob diseases by tonsil biopsy. Lancet 1997;349:99-100.
13. Collinge J, Sidle KCL, Meads J, Ironside J, Hill AF. Molecular
analysis of prion strain variation and the aetiology of `new variant'
CJD. Nature 1996;383:685-90.
14. Bruce ME, Will RG, Ironside JW, McConnell I, Drummond D, Suttie A, et
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15. Cousens SN, Vynnycky E, Zeidler M, Will RG, Smith PG. Predicting the
CJD epidemic in humans. Nature 1997;385:197-8.
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Explaining the Unexplained in Clinical Infectious Diseases: Looking Forward
Bradley A. Perkins* and David Relman†
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; and
†Palo Alto VA Medical Center, Palo Alto, California, USA
---------------------------------------------------------------------------
We examined the need to improve our ability to explain the unexplained in
clinical infectious diseases, primarily through improvements in diagnostic
technology. Part of the motivation for this effort came from an Emerging
Infectious Disease Program (funded by the National Center for Infectious
Diseases, Centers for Disease Control and Prevention [CDC]) to conduct
surveillance for unexplained deaths and critical illnesses due to possibly
infectious causes. This project has found that the number of such patients
in the United States is substantial and that a probable causative agent can
be identified in only a small fraction of these patients.
John Bartlett, Johns Hopkins University, Baltimore, Maryland, and Sherif
Zaki, CDC, Atlanta, Georgia, addressed the current status and offered their
perspectives on pneumonia, particularly acute respiratory distress syndrome
(ARDS) and hemorrhagic pneumonia, syndromes frequently associated with
unexplained critical illness. Greg Kovacs, Stanford University, Stanford,
California, and Michael Eisen, Stanford University School of Medicine,
Stanford, California, presented possible technologies and approaches to
improving diagnostic capabilities—a sensitive biologic detection system
(for toxins and host gene expression responses) for diagnosing infectious
diseases.
Pneumonia—Evolving Diagnostic Practices
Pneumonia, the most common infectious cause of death in the United States,
accounts for approximately 45,000 deaths annually. In large hospital-based
studies, no causative agent can be identified in 35% of community-acquired
pneumonia cases. In actual practice, this proportion is probably 50% to
75%.
Over the last three decades, the proportion of community-acquired pneumonia
cases in which Streptococcus pneumoniae was isolated has substantially
declined. In the 1970s, the proportion was 62%; in the 1980s, 40%; and in
1991, 18%. Why has the recovery of pneumococci from patients with
community-acquired pneumonia changed so dramatically? Have the causes of
community-acquired pneumonia changed? Standard "gumshoe" microbiology to
isolate pneumococci has taken a devastating hit in the 1990s due to
outsourcing of microbiology services or just decreased emphasis on standard
microbiology practices (e.g., collection and handling of clinical
specimens). Newly recognized agents such as Legionella pneumophila may also
explain some of the decrease in the proportion of pneumococci isolated.
Recommendations for the evaluation and management of community-acquired
pneumonia, developed by the Infectious Disease Society of America, were
published in the April issue of Clinical Infectious Diseases. These
recommendations detail diagnostic tests as well as inadequacies in
diagnostic technologies for several of the common causes of
community-acquired pneumonia, including Chlamydia pneumoniae, L.
pneumophila, and Mycoplasma pneumoniae.
Pathologic Approach to the Diagnosis of Infectious Causes of Pulmonary
Hemorrhage and Acute Respiratory Distress Syndrome
Pathologists should recognize patterns of tissue injury (especially in the
lung parenchyma) that react in specific and predictable ways. This approach
narrows diagnostic options and focuses testing efforts. Acute lung injury
(e.g., diffuse alveolar damage or ARDS) and air space filling patterns
(e.g., hemorrhage and pulmonary edema) of lung injury are two important
patterns manifesting infectious disease. Examples include diffuse alveolar
damage associated with adenovirus infection (smudge cells may be seen);
measles (giant cells); respiratory syncytial virus (RSV) infection;
influenza infections; Rocky Mountain spotted fever; typhus; legionnella;
mycoplasma; and hemorrhage associated with aspergillosis, mucormycosis,
leptospirosis, dengue, yellow fever, Lassa, and Ebola virus infection. The
recognition of these patterns (combined with application of special stains,
immunohistochemical reagents, and in situ hybridization) is a powerful tool
in the diagnosis of unexplained critical infectious diseases.
Two examples of the application of these combined methods to the
identification of infectious agents are the 1993 hantavirus epidemic in the
southwestern United States and the 1995 leptospirosis epidemic in
Nicaragua. In the hantavirus epidemic, healthy young adults contracted
fever and rapidly progressive pulmonary disease consistent with ARDS, and
many died within days of the onset of illness. Testing for a wide variety
of agents was negative. Lung tissue showed interstitial pneumonitis and
interalveolar edema; these patterns were consistent with viral pneumonia or
toxic change. After serum samples from these patients were found to
cross-react with known hantaviruses, antibodies were used to demonstrate
hantavirus in the lung, kidney, and muscle tissues. In the leptospirosis
epidemic, after heavy rains in northern Nicaragua, a number of persons
became ill with fever, headache, muscle aches, hemorrhage, and severe ARDS;
no prominent renal or hepatic manifestations were observed. Initial testing
focused on hantavirus, dengue, and other viral agents, but results were
negative. Pathologic examination of tissue from fatal cases showed
pulmonary hemorrhage and diffuse alveolar damage, as well as renal and
hepatic changes. In the 1980s, reports of leptospirosis epidemics in Korea
and China prompted investigators to develop an immunohistochemical test for
leptospirosis; the disease was subsequently found in kidney, liver, and
lung specimens of Nicaraguan patients.
Novel Bioassay for Detecting Toxin-Mediated Illness
The impetus for this project has been twofold: military detection of
chemical and biological warfare agents and pharmaceutical screening. Cells
are cultured on silicon chips, and their response to toxins is monitored in
several ways (e.g., action potential for electrically active cells,
impedance, and motility). These systems complement other approaches because
they allow detection of unknown or unrecognized toxins. A cell monolayer is
incredibly responsive because of its diffusion characteristics; this
responsiveness can be tuned by selection of cells and through engineering.
The use of cocultures can allow diversity in detection and response
characteristics. In addition to detecting chemical and biological warfare
agents, these systems can screen for antidotes by challenging the system
with the toxin and adding a putative antidote. Pharmaceutical companies are
interested in using this system for early screening of drug actions on cell
physiology.
Chick myocardial cells and NG108 neuroblastoma hybrid cell lines were used
to examine the shape and frequency of action potentials. Exposure of these
cells to agents with known effects on cell physiology (e.g., epinephrine,
verapamil, and tetrodotoxin) causes predictable changes (depending on the
interaction of these toxins with transmembrane channels) on the shape of
action potential curves when deviation from baseline is used as the
internal control on response. Impedance measurement (alteration in
electrical current after passage through a cell) can also be used to
reflect changes in the cell membrane as a result of exposure to a toxin.
The effect of toxins on the cytoskeleton can also be measured by cell
motility through impedance. When this technology was first developed, it
required approximately 1 m(sup 3) of electronics support, but with silicon chips
a laptop computer can now support the operation. A Windows application can
handle the data processing, and the technology can be transferred to other
laboratories.
Cellular Scouts: Genome-Wide Expression Monitoring of Peripheral Blood to
Detect and Characterize Pathogens
Using an easily constructed robot, we have been building DNA microarrays in
which each dot represents different open reading frames. In the fully
sequenced genome of Saccharomyces cerevisiae, there are 6,200 dots or open
reading frames. The Human Genome Project has identified approximately
50,000 distinct cDNA sequences, and we have been using microarrays with
approximately 15,000 of these. By the end of 1998, we will have all 50,000
genes on a microarray. For these assays we use a control and an
experimental sample. From these samples, we isolate polyadentylated RNA by
using any of a variety of kits, and then make fluorescently labeled cDNA
copies, with each of the two samples labeled with a different color (e.g.,
one green and the other red). RNA is degraded to avoid any confounding
signals; the samples are mixed and then hybridized to the microarray. The
microarray is imaged by using a scanning laser confocal microscope, and
through a process of quantitation, the relative representation of every
gene in sample 1 versus sample 2 is calculated. These data provide a very
high resolution fingerprint of what is going on in any cell(s) of interest.
So when a sample from a healthy person is compared with one from an ill
person, differences in gene expression should be sufficiently unique to
diagnose particular infections.
First, however, we would like to know that cells respond to internal and
external stimuli by at least some differences in expression of their genes,
that specific stimuli result in distinct gene expression patterns, and that
the response to stimuli evolves in a stereotypic temporal manner. Ideally,
we would like not only to diagnose a particular infection but also to
determine the stage of that infection. Preliminary data from our laboratory
support these hypotheses. The patterns of human gene response to different
stimuli, including T-cells stimulated with mitogens, cells exposed to DNA
damaging agents, and cells infected with polio and cytomegalovirus have
distinct DNA expression patterns, or "bar codes," that change over time.
Although we have not processed a wide selection of infectious agents, we
have evaluated approximately 60 distinct human tumor cell lines using a
common control cell line. When we used these data for phylogenetic
reconstruction, we found very good clustering with respect to the tissue of
origin. Specific signatures are related to central nervous system tumors,
kidney tumors, melanomas, and leukemias.
We would like to focus on the use of peripheral blood cells as a sort of
infectious disease sensor. There are a number of reasons to believe that
this may work. We have data from human lymphocytes harvested from whole
blood (where one sample is exposed to interleukin-2 and the other is not)
and we can demonstrate many changes in gene expression. To make this
approach useful, we will need a broad range of gene array data from persons
with known causes of illness.
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Malaria: A Reemerging Disease in Africa
Thomas C. Nchinda
World Health Organization, Geneva, Switzerland
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A recent upsurge of malaria in endemic-disease areas with
explosive epidemics in many parts of Africa is probably caused
by many factors, including rapidly spreading resistance to
antimalarial drugs, climatic changes, and population movements.
In Africa, malaria is caused by Plasmodium falciparum and is
transmitted by Anopheles gambiae complex. Control efforts have
been piecemeal and not coordinated. Strategies for control
should have a solid research base both for developing
antimalarial drugs and vaccines and for better understanding
the pathogenesis, vector dynamics, epidemiology, and
socioeconomic aspects of the disease. An international
collaborative approach is needed to build appropriate research
in a national context and to effectively translate research
results into practical applications in the field. The
Multilateral Initiative for Malaria in Africa can combine all
of the above strategies to plan and coordinate partnerships,
networking, and innovative approaches between African
scientists and their Northern partners.
The global malaria eradication program of the 1950s and 1960s suffered
serious setbacks in the early 1970s, and the disease was slowly increasing
in areas of Asia and South America where the number of cases had been
reduced to low levels. This article discusses malaria and, more
specifically, malaria in Africa, where the global eradication program was
never started and the disease is reemerging at an alarming and
unprecedented rate.
The Disease
Malaria in humans is caused by a protozoon of the genus Plasmodium and the
four subspecies, falciparum, vivax, malariae, and ovale. The species that
causes the greatest illness and death in Africa is P. falciparum. The
disease is transmitted by the bites of mosquitoes of the genus Anopheles,
of which the Anopheles gambiae complex (the most efficient) is responsible
for the transmission of disease in Africa. Fever is the main symptom of
malaria. The most severe manifestations are cerebral malaria (mainly in
children and persons without previous immunity), anemia (mainly in children
and pregnant women), and kidney and other organ dysfunction (e.g.,
respiratory distress syndrome). Persons repeatedly exposed to the disease
acquire a considerable degree of clinical immunity, which is unstable and
disappears after a year away from the endemic-disease environment. Immunity
reappears after malarial bouts if the person returns to an endemic-disease
zone. Most likely to die of malaria are persons without previous immunity,
primarily children or persons from parts of the same country (e.g., high
altitudes) where transmission is absent, or persons from more
industrialized countries where the disease does not exist.
Why Is Malaria Reemerging?
In the last decade, the prevalence of malaria has been escalating at an
alarming rate, especially in Africa. An estimated 300 to 500 million cases
each year cause 1.5 to 2.7 million deaths, more than 90% in children under
5 years of age in Africa (1). Malaria has been estimated to cause 2.3% of
global disease and 9% of disease in Africa (1); it ranks third among major
infectious disease threats in Africa after pneumococcal acute respiratory
infections (3.5%) and tuberculosis (TB) (2.8%). Cases in Africa account for
approximately 90% of malaria cases in the world (1). Between 1994 and 1996,
malaria epidemics in 14 countries of sub-Saharan Africa caused an
unacceptably high number of deaths, many in areas previously free of the
disease (2). Adolescents and young adults are now dying of severe forms of
the disease. Air travel has brought the threat of the disease to the
doorsteps of industrialized countries, with an increasing incidence of
imported cases and deaths from malaria by visitors to endemic-disease
regions. The estimated annual direct and indirect costs of malaria were
US$800 million in 1987 and were expected to exceed US$1.8 billion by 1995
(3).
A number of factors appear to be contributing to the resurgence of malaria:
1) rapid spread of resistance of malaria parasites to chloroquine and the
other quinolines; 2) frequent armed conflicts and civil unrest in many
countries, forcing large populations to settle under difficult conditions,
sometimes in areas of high malaria transmission; 3) migration (for reasons
of agriculture, commerce, and trade) of nonimmune populations from
nonmalarious and usually high to low parts of the same country where
transmission is high; 4) changing rainfall patterns as well as water
development projects such as dams and irrigation schemes, which create new
mosquito breeding sites; 5) adverse socioeconomic conditions leading to a
much reduced health budget and gross inadequacy of funds for drugs; 6) high
birth rates leading to a rapid increase in the susceptible population under
5 years of age; and 7) changes in the behavior of the vectors, particularly
in biting habits, from indoor to outdoor biters.
What Knowledge Is Needed for Effective Control?
Continental sub-Saharan Africa was never a part of the global malaria
eradication program. The severity of the disease, the density and
efficiency of An. gambiae, the problem of eradicating the disease over such
a large land mass with recurrent reinvasions, high costs, and subsequent
maintenance must have all contributed to the lack of will to undertake an
eradication program. Also, the eradication program period coincided with
the colonial and immediate postcolonial period, during which little or no
indigenous capacity was available to initiate and sustain malaria
eradication. After a period of laissez faire regarding malaria control,
these countries have had to face the reemergence of the disease. Important
questions about control include the following. Is there enough knowledge
about the disease and its determinants? Are there enough tools? Are
existing resources adequate? Are governments and populations of
endemic-disease countries adequately prepared?
Knowledge About the Disease and Its Determinants
Falciparum malaria is a complex disease with a patchy nonuniform
distribution and clinical manifestations that vary from one area to another
within an endemic-disease zone, often showing space-time clustering of
severe malaria in the community (4). The relationship between fevers,
clinical disease, anemia, and cerebral malaria remains the subject of
current research. The determinants of severe life-threatening malaria need
further elucidation. Present research, focusing on the disease rather than
the infection and the dynamics of its transmission, is bringing in new
vision about the disease, particularly the immunologic aspects. Persons
with asymptomatic parasitemia constitute an important reservoir. The
epidemiology of malaria (particularly the relationship between the clinical
patterns of the disease in different locations, the pattern of severe
disease, and causes of deaths due to malaria) needs future research (5).
Tools for Malaria Control
The present strategy for malaria control, adopted by the Ministerial
Conference on Malaria in Amsterdam in 1992, is to prevent death, reduce
illness, and decrease social and economic loss due to the disease (6). Its
practical implementation requires two main tools: first, drugs for early
treatment of the disease, management of severe and complicated cases, and
prophylactic use on the most vulnerable population (particularly pregnant
women); second, insecticide-treated nets for protection against mosquito
bites. Each tool has its own problems in regard to field implementation.
Chloroquine remains the first-line therapy for malaria. However, the
alarming increase in resistance in eastern and southern Africa requires
that sulfadoxine-pyrimethamine replace chloroquine as the first-line drug.
Currently, 20% to 30% of strains are highly resistant (RIII) with in vivo
levels of 40% to 60%. Resistance has been spreading westward, attaining
levels of 20% to 35% in West Africa. Chloroquine remains the drug of choice
in most of sub-Saharan Africa.
Resistance to mefloquine, another first-line drug, developed in the early
1980s, was noticed soon after its introduction and is now almost at the
same level as chloroquine. Sulfadoxine-pyrimethamine (Fansidar, Hoffman la
Roche) is the second-line drug in many countries of West and Central
Africa, but so much resistance appears to be rising in countries of East
Africa that atovaquone/dapsone (Malarone, Glaxo Wellcome) is being
developed as a replacement. Intravenous quinine is still the main therapy
for cerebral malaria, although resistance is increasing. Development by the
African strains of malaria parasites of the pattern of drug resistance now
seen in Southeast Asia would be a major disaster.
More research is needed. For example, it is necessary to initiate
systematic monitoring of drug resistance in Africa using standardized
methods. Drug efficacy studies using in vivo methods have now been
standardized by the World Health Organization (WHO)/Regional Office for
Africa (AFRO) and carried out in a large number of countries in West,
Central, and East Africa. Sentinel sites have also been established for
monitoring resistance. No new methods are being developed. The feasibility
of using polymerase chain reaction techniques should be explored. Also,
management guidelines should be developed concerning when and under what
conditions to change the treatment regimen for different levels of
resistance at the district, regional, and central level. Development and
field testing of inexpensive, effective new malaria drugs are urgently
needed to replace present drugs when resistance patterns make them
unusable. Drugs developed because of the more serious problem of drug
resistance in Asia should be field tested in Africa. The most promising
ones, artemisinin and its derivatives artemether, arteether, and
artesunate, are being tested for use in cerebral malaria and cases of
proven resistance to chloroquine (12); some are already used in some
countries.
Research carried out in Dakar (7) demonstrated the efficacy of
insecticide-treated nets for reducing infant death; subsequent large-scale
multicenter studies in six countries across Africa confirmed this finding
(8-10). However, costs of the nets and treatment still inhibit wide-scale
use. Ongoing research seeks ways of reducing these costs, such as social
marketing, possible involvement of the private sector, cost-effective
methods for net treatment, the most appropriate nets, and proper
procurement of insecticides and treatment of the nets. Eventually, the
long-term effects on natural acquisition of partial immunity to malaria in
endemic-disease areas should be evaluated. The old vector-control method of
house spraying persists in some countries. The relative merits and
cost-effectiveness of house spraying versus the use of treated nets should
be evaluated.
The Challenge of Malaria Control to Communities and Governments
The best tools will not necessarily lead to malaria control. African
populations have traditional perceptions about disease causation and
management. Some diseases are considered suitable for management by western
medicine, while others are considered the exclusive domain of local
traditional health practitioners. Decisions to seek western medicine for
any illness are often considered a last resort. Studies on health-seeking
behavior, perceptions of malaria, treatments, and decision making for
health care at the household level are crucial to malaria control. Such
studies must be accompanied by improved public awareness of the importance
of seeking appropriate treatment and complying with recommended regimens.
Management of disease in the household devolves on mothers. Fever remains
the most recognized symptom of malaria. Studies are ongoing to determine
the proportion of fevers actually due to malaria. Mothers should be taught
to recognize the symptoms of malaria, to provide home management, and to
know when to refer cases to health centers. Four countries in Africa have
developed and tested teaching guides to facilitate home management of
malaria (11). Also, guidelines for the management of fever at the periphery
have been developed and field tested within the Sick Child Initiative and
have been recommended for wide-scale application. Socioeconomic and
community studies are needed to understand the extent to which the
communities will participate in new malaria control measures. Finally, cost
recovery of health care, including costs of drugs (the Bamako Initiative),
has been the subject of many recent studies and probably holds the key to
health care in rural populations.
Some study results indicate an initial fall in use of services following
the introduction of cost-recovery schemes (12). However, a recent study
indicates the opposite. Community health workers were trained to administer
prepackaged antimalarial drugs only when paid. They also received direct
remuneration for their work rather than being supported by the village on a
voluntary basis (13). This plan seems to have increased attendance. This
subject needs large-scale multicenter studies.
Governments' ResponsePeripheral Health Services
Health service organization, function, and governing policies are important
to malaria control. Health policy and systems research have been recently
identified as neglected areas of research in need of international effort
(1). Many studies are researching different ways to integrate vertical
malaria control programs into the general health-care system. Economic
evaluation of different interventions is important, and the techniques are
continually being refined and improved. They require much local capacity
since they tend to be country specific. Studies in this area have now
caught up with the current trend favoring decentralization of services,
giving more power to the districts. Such studies include ways of improving
case management where health services have been decentralized, sustaining
effective interventions, and ensuring that drug supply chains function
optimally. Extensive research is examining health sector reform on malaria
control (12). Health sector reform holds great potential for controlling
malaria and all other diseases, as it is the focal point of the central and
local governments and the populations themselves. Other needed research
includes different health policies, access to health services, and the
issues of equity in health care.
Is There a Place for Biomedical Research?
If the emphasis appears to be on epidemiologic and socioeconomic research
and studies on health policies and systems, it is because these results
have immediate importance to malaria control. The argument is for better
use of existing tools. However, tools alone will not provide all the
knowledge needed for sustainable malaria control. Recent research by the
Wellcome Trust and the National Institutes of Health on sequencing the
genome of P. falciparum is likely to lead to development of new
antimalarial drugs and vaccines. Similarly, DNA technologies are being used
to search for candidate molecules for vaccines and new targets for drug
development.
The development of a malaria vaccine is still in the laboratories, and no
effective vaccine is in sight despite promising candidates. Subsequently,
all candidate vaccine trials must be closely linked to studies on how
humans acquire immunity and the correlation between protective immunity and
immunologic assays. Such studies should be carried out longitudinally in
multiple sites where future vaccines will be tested.
On the vector side, studies in Mali have shown that malaria transmission in
this Sahel country is maintained by a relay transmission pattern, whereby
the three main vectors appear at different times of the year, thus ensuring
that vectors are always present (Y. Toure, pers. comm.). More research is
in progress concerning the potential of using genetic engineering to make
the main malaria vector, An. gambiae, refractory to the malaria parasite
and releasing this refractory parasite into the wild population to replace
the active vectors. Despite potential ethical problems, this approach
probably constitutes a long-term future method for interrupting malaria
transmission (14). Finally, the much-neglected issue of the pathogenesis of
malaria anemia both in children and pregnant women, as well as the link of
anemia in pregnancy and HIV/AIDS, needs further study and is likely to be
multifactorial.
Mapping malaria transmission intensity using geographic information systems
and geographic positioning systems has developed into a Pan-African
research collaboration for Mapping the Malaria Risk in Africa, which has
received international funding. It plays a major role in time-spatial
mapping of malaria across the continent with a strong potential for
predicting malaria epidemics (15) and monitoring control.
What Is the Response of the World Health Organization?
WHO developed global and regional strategies for malaria control after the
Ministerial Conference on Malaria in Amsterdam in 1992. WHO/AFRO has
multiplied efforts to encourage countries to embark seriously on malaria
control. A WHO/AFRO Task Force for Malaria comprising a selected sample of
malaria control managers, malaria experts from Africa, and technical
representatives from bilateral and multilateral agencies funding malaria
control in Africa was set up in 1994. This task force has met regularly to
provide guidance on malaria control strategies and to recommend criteria
for monitoring and evaluation as well as operational research. Some of
these agencies have recently increased their malaria control funding
directly to some countries of Africa; others have preferred funding through
the regional office.
In addition, the WHO Director General made a generous grant of US$10
million from the WHO regular budget for 1997 for intensified malaria
control efforts. Momentum is building, strongly supported by the World
Bank, for more concerted efforts at malaria control.
The Way Forward
The Multilateral Initiative on Malaria in Africa (MIM) was created in Dakar
in January 1997 from the realization that success in controlling malaria in
the future would be greatly enhanced by cooperation and collaborative
efforts in research to support strategies for control (5). MIM capitalized
on the important 1992 Ministerial Conference, which led to the adoption of
a Global Plan of Action for Malaria Control and the World Health Assembly
Resolution on this subject (WHA 49.11), urging increased efforts on malaria
control. Composed of scientists from Africa and their colleagues from
industrialized countries as well as representatives from major funding
agencies, MIM plans to facilitate collaboration between governments,
research scientists, research funding agencies, and the private
(pharmaceutical industry) sector for concerted action through research to
combat malaria.
Like other diseases of low-income countries, malaria has been grossly
underfunded. From 1990 to 1992, $58 million a year was spent on malaria
research, while $56 billion was spent on health research worldwide.
Expressed as research investment per death, malaria research receives about
US$42 per fatal case, much less than for other diseases such as HIV/AIDS
(US$3,270) and asthma (US$789) (3). Rather than the duplicative efforts of
the past, MIM encourages a common goal with common research priorities,
which should create a greater spirit of cooperation.
Strengthening Research Capability
MIM took a firm stand on indigenous capacity building for malaria research
in Africa, an important prerequisite for sustainable research and control
of malaria in that continent. Training would be carried out in Africa as
far as possible but not exclusively so. Training would be carried out for
all health-care workers within the malaria research and control pyramid,
including Ministry of Health personnel and those in research institutes and
universities, with no exclusion. Flexible training programs would be
developed to meet the needs of individual research centers and countries. A
good start has been made. Using funds provided late in 1997 to WHO's
Tropical Diseases Research Programme, a task force was set up for Malaria
Research Capability Strengthening in Africa. The money funded North/South
and South/South collaborative research in malaria. All the principal
investigators were to be from Africa. Training was central to the projects
so that more hands-on and practical research training would be given to
trainees, and practical refresher training and technology transfer would be
given to experienced scientists.
Research centers also need to be strengthened. Laboratories need
refurbishing and equipment and supplies (including computer equipment and
software), and vehicles are needed for field studies. Suitable research
careers should be created to encourage the best scientists to remain in
research.
Because scientific isolation constitutes a major constraint to African
scientists, communication facilities need urgent attention. One of MIM's
highest priorities is to enhance the capacity of African scientists to
communicate electronically with each other and with colleagues around the
world and to access needed scientific information from local and remote
libraries and the Internet. NIH's National Library of Medicine is playing a
lead role in this critical area.
The Future
Malaria is an important social, economic, and developmental problem
affecting individuals, families, communities, and countries. The best
chance for successfully combating the disease requires a collaboration
particularly of those responsible for control and research. Such
collaboration, particularly between South and North, is being actively
developed, and MIM presents itself as a worthwhile initiative (16).
Important factors are 1) placing the control strategy on a strong research
base, 2) strong international collaboration, and 3) sustained government
support.
Smallpox was eradicated because of the development of freeze-dried vaccine,
the development of the multiple-use nozzle jet injector and bifurcated
needle, and the replacement of mass vaccination by selective vaccination,
coupled with a strong international effort. Onchocerciasis is being
controlled because research results were immediately applied to control.
Translating research findings into control methods has also been pursued
for Chagas disease and leprosy. Concerted action between the research and
control communities is needed to ensure that malaria follows the same path.
MIM strongly advocates this approach. Research must be a constant feature
throughout the entire process of malaria control.
Dr. Nchinda is senior health specialist at the Global Forum for Health
Research based at the World Health Organization headquarters in Geneva. His
research interests are in tropical diseases research and control,
particularly malaria, training and utilization of health personnel,
research capacity strengthening, health services research, and organization
of community health services.
References
1. World Health Organization. Investing in health research for
development. Report of the Ad Hoc Committee on Health Research
Relating to Future Intervention Options. Geneva:The Organization;
1996. Report No.: TDR/Gen/96.1
2. Harare declaration on malaria prevention and control in the context of
African economic recovery and development. In: Proceeding of the 33rd
Ordinary Session of the Assembly of Heads of State and Government,
Organization of African Unity; 1997 2-4 June; Harare, Zimbabwe.
3. Anderson J, MacLean M, Davies C. Malaria research: an audit of
international activity. Prism Report No. 7, The Wellcome Trust; 1996.
4. Snow RW, Schellenberg JR, Peshu N, Foster D, Newton CR, Witstanley PA,
et al. Periodicity and space-time clustering of severe childhood
malaria on the coast of Kenya. Trans R Soc Trop Med Hyg
1993;87:386-90.
5. Final report: International Conference on Malaria in Africa, 6-9
January 1997, Dakar, Senegal. [document online] Available from: url:
http://www.niaid.nih/dmid/malafr/.
6. World Health Organization. Control of Tropical Diseases: 1. Progress
Report. Geneva: The Organization, Division of Control of Tropical
Diseases; 1994. Report No.: CTD/MIP/94.4
7. Alonso PL, Lindsay SW, Armstrong JRM, Conteh M, Hill AG, David PH, et
al. The effect of insecticide-treated bed nets on mortality of Gambian
children. Lancet 1991;337:1499-502.
8. Nevill CG, Some ES, Mung'ala VO, Mutemi W, New L, Marsh K, et al.
Insecticide treated bednets reduce mortality and severe morbidity
among children in the Kenyan Coast. Trop Med Int Health 1996;1:139-46.
9. Binka FN, Kubaje A, Adjuik M, Williams LA, Lengeler C, Maude CH, et
al. Impact of Permethrine impregnated bednets on child mortality in
Kassena-Nankana district of Ghana: a randomized controlled trial. Trop
Med Int Health 1996;1:147-54.
10. Lengeler C, Cattani J, de Savigny D, editors. Net gain: a new method
for preventing malaria deaths. Ottawa, Canada: International
Development Centre/World Health Organization; 1996.
11. World Health Organization. Toward healthy women counseling guide:
ideas from the gender and health research group. Geneva: The
Organization, UNDP/World Bank/WHO Special Programme for Research and
Training in Tropical Diseases (TDR). Report No.: TDR/GEN/95.1
12. World Health Organization. Tropical diseases research: progress
1995-96. 13th Programme Report. Geneva: The Organization, UNDP/World
Bank/WHO Special Programme for Research and Training in Tropical
Diseases(TDR), Geneva.
13. Pagnoni F, Convelbo N, Tiendrebeago H, Cousens S, Esposito F. A
community-based programme to provide prompt and adequate treatment of
presumptive malaria in children. Trans R Soc Trop Med Hyg
1997;91:512-7.
14. Carlson J, Olson K, Higgs S, Beaty B. Molecular genetic manipulation
of mosquito vectors. Annu Rev Entomol 1995;40:359-88.
15. Omumbo J, Ouma J, Rapouda B, Craig M, le Sueur D, Snow RW. Mapping
malaria transmission intensity using geographic information systems:
an example from Kenya. Ann Trop Med Parasitol. In press 1998.
16. Mons B, Klasen E, van Kessel R, Nchinda T. Partnerships between South
and North crystallizes around malaria. Science 1998;279:498-9.
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Vaccine-Preventable Diseases
Alison C. Mawle
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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The panel addressed four main areas of vaccine development and use:
diseases of public health importance for which no vaccine is available;
diseases for which an existing licensed vaccine is not optimal and
alternative vaccines are under development; diseases for which a vaccine
exists but is not being used optimally; and diseases requiring vaccines of
specialized or limited use, such as those needed for controlling outbreaks
or for military use. The specific diseases chosen to illustrate each area
were malaria, influenza, meningitis, and filovirus infections (Ebola and
Marburg), respectively.
Lee Hall, National Institute of Allergy and Infectious Diseases, addressed
the basic challenges in developing a malaria vaccine. The historical norm
of vaccine development has been an empirical process; in contrast, modern
vaccines take advantage of basic knowledge of the organism and of the
immune response to it. In vaccine development, certain elements are
prerequisite: demonstrable protective immunity and intimate knowledge of
the organism's life cycle, including the DNA sequence. Vaccine development
has three potential goals: prevent infection, prevent disease, and prevent
transmission. A successful vaccine may address any or all these areas; for
malaria, a vaccine able to perform any of these would have a significant
impact. Vaccine development, often thought of as a flow, is in fact an
iterative process; it addresses scientific, technical, manufacturing, and
clinical issues and is affected by economic, political, and social issues
usually outside the scientific sphere of influence. Several downstream gaps
in vaccine development include resource limitation, lack of
standardization, and problems in clinical and industrial interest.
Claude Hannoun, Institut Pasteur, addressed problems in influenza vaccine
development. Influenza, the quintessential emerging infectious disease,
needs a new vaccine each year to protect against the predominant strains.
The disease poses additional challenges; one is the need for vaccine
against a potential pandemic strain, particularly a pandemic strain whose
epidemiologic characteristics are different from those of usual strains
(e.g., the 1918 strain killed young adults). Vaccine production problems
pose another challenge. Identifying an appropriate seed strain can delay
initiation of production for 4 to 6 months after the need for a vaccine has
been identified, and growing sufficient quantities of vaccine is difficult.
The issue of an appropriate vaccine regimen (one dose or two) was also
addressed. The many vaccination issues involved in a pandemic situation
make the adoption of a credible pandemic plan imperative. The emergence of
the H5N1 strain in Hong Kong has underlined this imperative.
Brad Perkins, Centers for Disease Control and Prevention, presented the
challenge of the African meningitis belt, where periodic large epidemics
affect approximately 1% of the population with a 10% death rate. Since the
current vaccine does not confer lasting protection, prediction of these
epidemics can trigger vaccination campaigns to prevent deaths. A model
using an epidemic threshold of 15 cases per 100,000 demonstrated potential
lives saved. Obstacles to the use of the vaccine include inadequate
surveillance, high cost of the vaccine, inadequate delivery systems, and
inadequate vaccine supply.
Vaccines for agents such as Marburg and Ebola were discussed by Alan
Schmaljohn, U.S. Army Medical Research Institute of Infectious Diseases.
Limited-use vaccines do not have a global market but are potentially
important against the threat of biological weapons or epidemics. These
vaccines have unique problems, such as inadequate efficacy testing (since
there is no disease-endemic area) and high production costs (since there is
no target population).
All the presentations addressed public policy issues: who will use the
vaccine and under what circumstances, what is the time frame for vaccine
development (short-term versus long-term), what is the cost of a vaccine
(who bears the brunt of development costs), how are these costs recouped,
and what is the role of partnerships in determining vaccine need and use.
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Global Tuberculosis Challenges
Kenneth G. Castro
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
------------------------------------------------------------------------
Mario Raviglione, World Health Organization (WHO), described the
epidemiology of global tuberculosis (TB) using surveillance data available
to WHO from 212 countries and data from a recent survey of antituberculosis
drug resistance in 32 countries. Countries were categorized according to
the degree of TB directly observed treatment strategy (DOTS)
implementation. Performance of national TB programs was assessed by using
treatment outcome indicators. In 1996, 3.8 million TB cases (887,731 from
areas with DOTS) were reported to WHO. In developing countries, the bulk of
TB cases are found in all age groups of native-born populations, while in
many industrialized countries a large proportion of TB cases are in
foreign-born residents. In countries of the former Soviet Union, TB cases
and deaths have doubled in just a few years. Drug resistance and HIV
infection related to TB are found only in limited foci. Acquired
multidrug-resistant TB (MDRTB) was present in 27% to 54% of
culture-positive TB cases from the Baltic countries and Russia. The effect
of the HIV epidemic on TB has been major in Africa, where HIV
seroprevalence among TB cases is 50% to 70% and TB case notifications have
at times tripled. Countries with inadequate TB control are particularly
exposed to the consequences of both epidemics. In Southeast Asia, cases are
increasing, and MDRTB is common in Thailand, China, and Vietnam.
One hundred eighty-one countries and territories (97% of the global
population) have reported on the status of DOTS to WHO. Of these, 96
implemented DOTS (63 countrywide). Approximately 32% of the global
population lives in areas where DOTS is available. Twenty countries have
adopted DOTS since the 1996 survey, and an additional 9% of the global
population were benefitting from it. However, most of these new countries
had small populations; DOTS was only slowly implemented in countries with
high TB prevalence. In areas that used DOTS, treatment outcome evaluation
remains high (94%), and treatment success rose from 76% in 1994 to 78% in
1995. In areas that did not use DOTS, 45% of reported TB cases were not
evaluated, and treatment success remained low (45%). Among the 22 countries
with the highest TB prevalence, six showed progress in DOTS implementation,
seven showed little progress, and nine did not implement DOTS. In summary,
TB remains an important public health problem in many areas of the world
where DOTS has not been implemented. Because treatment outcomes were better
in countries where DOTS has been used, the strategy needs to be expanded
rapidly and new tools to facilitate its implementation need to be
developed.
Barry Bloom, Howard Hughes Medical Institute, described advances in TB
vaccine development. The available bacillus Calmette-Guerin (BCG) vaccine
has a demonstrated efficacy ranging from no protection to 80% protection.
Most recently, a meta analysis estimated that the overall efficacy of BCG
is 50%. Because of case reports of disseminated BCG infection, this vaccine
is contraindicated in immunocompromised persons, and safer and more
efficacious vaccines are clearly needed. Identifying such new vaccines for
use in humans will take several years. However, recent advances in this
area provide optimism. Recent research activities have improved our
understanding of the immunologic response to Mycobacterium tuberculosis and
identified major protein antigens of M. tuberculosis and recombinant BCG
forms that overexpress protective antigens. Additionally, avirulent
auxotrophic mutants of both BCG and M. tuberculosis have been used in
animal models. The recent sequencing of the M. tuberculosis genome has
presented additional opportunities to identify virulence factors that could
be deleted and other target sites that could be genetically engineered. DNA
constituents can also be used to develop candidate vaccines. In animal
studies, subunit vaccines consisting of pooled mycobacterial
culture-filtrate proteins have been protective. Auxotrophic mutants may
also prove useful in immuno-compromised patients, as may recombinant BCG
vaccines that secrete host-specific cytokines. Clearly, a major national
effort is required for TB vaccine development, recommendations on policies
and priorities, and cooperation between the government and private sector
in these efforts.
Christopher Murray, Harvard School of Public Health, described a
mathematical model developed to forecast the future impact of improvements
in TB prevention and control. Specifically, this model projected the number
of TB cases and deaths averted through the year 2050. Different scenarios
were simulated to project the effect of adding TB vaccines to existing
interventions. Six specific scenarios assessed the effect of vaccines (with
efficacy levels of 20%, 50%, and 80%) to protect from M. tuberculosis
infection, as well as the effect of vaccines of the same levels of efficacy
to protect latently infected persons from "breakdown" to active TB.
Although a TB infection vaccine with 20% efficacy would prevent more than
30 million TB cases, the best protection is obtained from a TB breakdown
vaccine with 80% efficacy, which would prevent almost 130 million TB cases.
The breakdown vaccine could be used in the large number of persons with
latent M. tuberculosis infection, now estimated at almost one third of the
world's population. Such anticipated gains justify the effort to develop
better TB vaccines.
Denise Garrett, Centers for Disease Control and Prevention, presented the
findings of recent tuberculin skin test studies regarding the risk for TB
among health-care workers in Thailand and Brazil. In Thailand, 35% of 911
health-care workers had a positive test at the 15-mm cutoff, while 69% were
positive at the 10-mm cutoff. BCG scar was associated with positive skin
test reaction at the lower cutoff value, but not at the 15-mm cutoff.
Additionally, tuberculin skin test reactivity correlated with more than 1
year's employment as a health-care worker, and with occasional or frequent
patient contact. In Brazil, 48% of 524 health-care workers had a reaction
of 10 mm, while 26% had a reaction of 15 mm. As in Thailand, BCG scar
correlated only with 10-mm skin test reactivity but not with 15-mm. Workers
with occasional or frequent patient contact were also more likely to have a
positive tuberculin test. Factors that appear to contribute to the risk for
TB in these workers include delays in the diagnosis of TB, inadequate
isolation practices, and lack of personal protection during high-risk
procedures. Important measures to reduce the risk for TB in these settings
include increasing the awareness and training of health-care workers about
the risk for TB, improving the ability to establish the diagnosis of TB by
smear microscopy, reducing the need for hospitalization of TB patients,
considering the establishment of chest clinics at separate times or in
separate areas, and improving ventilation by keeping windows open.
Laboratories should contain all needed safety features.
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Blood Safety
Mary E. Chamberland,* Jay Epstein,† Roger Y. Dodd,‡ David Persing,§ Robert
G. Will,¶ Alfred DeMaria, Jr.,# Jean C. Emmanuel,** Beatrice Pierce,†† and
Rima Khabbaz*
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †Food
and Drug Administration, Washington, D.C., USA; ‡American Red Cross,
Washington, D.C., USA; §Western General Hospital, Edinburgh, Scotland; ¶The
Mayo Clinic, Rochester, Minnesota, USA; #Massachusetts Department of Public
Health, Boston, Masschusetts, USA; **World Health Organization, Geneva,
Switzerland; and ††National Hemophilia Foundation, New York, New York, USA
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The blood supply in industrialized countries is safer than ever. However,
blood (a human tissue) is a natural vehicle for transmission of infectious
agents. In recent years, numerous pathogens have emerged in the United
States and worldwide with the potential to affect the safety of the blood
supply.
International Movement of Infectious Agents
Movement of transfusable blood and blood components between countries is
relatively uncommon. However, infectious agents can cross international
borders through immigration or travel. For example, malaria is an important
problem in much of the world, with an estimated 300 to 500 million cases
per year. On average, 1,000 cases are reported each year in the United
States, most in persons who travel to malaria-endemic areas. Only a small
number of cases (approximately three per year) are transmitted by exposure
to infected blood products. Current measures (which temporarily defer
donors with a history of origin in a malarious country, clinical malaria,
or travel to malaria-endemic areas) appear to be effective. Similarly,
Chagas disease, a vector-borne disease caused by the parasite Trypanosoma
cruzi, is endemic in parts of Central and South America and Mexico, where
infected persons can transmit the disease through transfusion. The
immigration of millions of persons from T. cruzi–endemic areas and
increased international travel have raised concerns about the potential for
transfusion-transmitted Chagas disease. Five cases of T. cruzi transmission
from transfusions have been reported in North America. Recent
seroprevalence studies showed that approximately 0.1% of blood donors
likely to have been born in or have traveled to disease-endemic countries
were seropositive for T. cruzi. Moreover, American Red Cross studies of
recipients of T. cruzi–seropositive blood and blood products showed no
evidence of transmission. Finally, variant forms of recognized pathogens
can potentially affect the safety of the blood supply. Current serologic
tests do not consistently detect HIV-1 group O infections, which are common
in some West and Central African countries but very rare (two cases) in the
United States. Efforts are under way to modify existing serologic tests to
improve detection of group O strains without compromising sensitivity for
the predominant group M viruses. As an interim measure, the Food and Drug
Administration has recommended that donors at increased risk for HIV-1
group O on the basis of residence and risk exposure be deferred from
donating blood or plasma.
Creutzfeldt-Jakob Disease and Blood Safety
Risk for transmission by transfusion is poorly characterized for a number
of emerging agents. One of these is Creutzfeldt-Jakob disease (CJD), a
rare, fatal neurodegenerative disease believed to be caused by an abnormal
form of prion protein. CJD has been transmitted iatrogenically through
human pituitary-derived growth hormones, human dura mater grafts, corneal
transplants, and contaminated surface electroencephalogram electrodes and
neurosurgical instruments. Incubation was as long as 30 years in some
cases. Concerns regarding bloodborne transmission of the CJD agent derive
primarily from laboratory studies, including animal models, which suggest
such a potential. However, no proven cases of blood transmission are
reported in humans, and accumulating epidemiologic information
(surveillance, follow-up of recipients of blood from donors who
subsequently developed CJD, and case-control data) indicates that the risk
(if any) for transmission of CJD by blood products is extremely small. At
present, CJD is considered a remote, theoretical risk.
In March 1996, health officials in the United Kingdom announced that the
agent responsible for the decade-old bovine spongiform encephalopathy
epizootic might have spread to humans. As of March 1998, 24 persons have
been reported with this apparently new variant form of CJD (nvCJD). The
possibility of nvCJD transmission through the blood supply has been
debated. Currently, this risk is theoretical. However, because the
infectious agent of nvCJD is new in humans, it may present risks that
differ from those of classic CJD. In addition, important differences have
been noted in the two diseases. For example, human spleen and tonsil
tissues contain abnormal prion protein in nvCJD but not in classic CJD. In
view of this uncertainty, U.K. health officials have undertaken a
conservative approach, including 1) withdrawal of blood products donated by
persons subsequently confirmed or strongly suspected to have nvCJD; 2)
discontinuation of the use of British plasma in plasma-derived products;
and 3) consideration of leukodepletion of all blood donations, in view of
experimental studies suggesting that B lymphocytes may play a role in the
development of scrapie.
Tick-Borne Agents and Transfusion Risk
In the United States, the most commonly reported transfusion-associated
tickborne infection is babesiosis. At least 21 reported cases of
babesiosis, mostly caused by Babesia microti but also by the more recently
recognized WA1-type Babesia parasite, have been transmitted by transfusion
of blood from asymptomatic infected blood donors. With the expansion of
deer populations (natural host of B. microti) in the northeastern United
States, the incidence of transfusion-transmitted babesiosis may increase.
The tick vector and animal reservoir of the Babesia more recently found in
the northwestern and western United States remain to be defined. The
parasite survives blood-banking conditions and is transmissible by
transfusion of red blood cells and platelet concentrates. Although
babesiosis classically causes a febrile illness with hemolytic anemia,
infection can also cause chronic asymptomatic or mildly symptomatic
parasitemia. Recent studies suggest that untreated persons have evidence of
B. microti DNA for longer periods, despite mild or absent symptoms, and may
transmit infection for months or possibly longer. The potential for
transmission of other tick-borne agents is unclear. Like babesiosis, Lyme
disease or ehrlichiosis (caused by an obligate intracellular gram-negative
rickettsia) may be asymptomatic or mildly symptomatic; spirochetemia or
rickettsemia can precede prodromal symptoms by 24 to 72 hours, making
transmission by transfusion a possibility. One case of transfusion-
transmitted Rocky Mountain spotted fever has been reported.
Summary
Since blood is a biologic product, it is unlikely that the risk for
transfusion-transmitted infection will ever be reduced to zero. The
approach to emerging infections associated with transfusion of blood and
blood products includes assessing the transmissibility of the agent by this
route; developing effective prevention strategies, including screening
tests and donor deferral policies; improving viral and bacterial
inactivation procedures; and surveillance for known, as well as emerging
and poorly characterized, transfusion-transmitted agents. Vigilance is
needed to help ensure proper balance between safety and the availability of
blood. Finally, vigilance needs to extend to the developing world, where
the basic elements to reduce transfusion-transmitted infections and systems
of disease surveillance are often not available.
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Confronting Emerging Infections: Lessons from the Smallpox Eradication
Campaign
William H. Foege
Emory University, Atlanta, Georgia, USA
------------------------------------------------------------------------
Ralph Waldo Emerson in 1860 said, "We learn geology the day after the
earthquake." Traditionally, the world learns prevention the day after the
epidemic. Today, we have the responsibility of preparing for the prevention
and control not only of known but also unknown conditions. Eradication is a
focused field exercise in which approaches have been tested and from which
public health lessons can be learned.
Lessons from Eradication
Calculated Risks
It is clear, in retrospect, that we didn't know how to eradicate smallpox
when the eradication effort began. Thirty years ago, in the middle of the
smallpox campaign in West and Central Africa (charged with ending
transmission in 20 countries in 5 years), we tried a new strategy,
converting from mass vaccination to surveillance and containment. Although
we were 1 1/2 years into the campaign when the strategy shift occurred, we
still reached the goal of zero cases on time and under budget. The lesson
is that we do not have the luxury of waiting until we know everything
before doing something. We are always called upon to make decisions with
insufficient information and make corrections midcourse.
Interdependence
Disease eradication campaigns illustrate the value of working as global
citizens rather than as a collection of national programs. First promoted
by the Soviet Union in 1958, smallpox eradication did not get the approval
of the World Health Assembly until 8 years later in 1966, when it became a
joint proposal of the Soviet Union and the United States. If we could form
this alliance during the cold war, how many alliances can we form now? No
country alone can prevent or control emerging infections.
Knowledge
We did not understand the limitations of smallpox transmission; we knew
nothing about fetishes or the role of nomads. As organisms, the
environment, people, and tools change, programs must change. Appropriate
response requires good epidemiologic analysis. The epidemiology, in turn,
can be no better than the facts assembled. Knowledge is dependent on the
information system; in public health, the surveillance system forms the
foundation of knowledge.
Vision
With eradication, the vision is no more cases. With emerging infections,
the vision is rapid, appropriate, effective response, being prepared to
protect the world because you are ready to act.
Performance
With eradication, to get global support, we must demonstrate that a disease
can be eliminated from a geographic area. With emerging infections, the
value of surveillance (for making decisions, for deciding on interventions)
must be demonstrated.
Humility
With all our experience, we have not gone far on the road to eradicating
disease. This knowledge keeps us humble. We have trouble outthinking a
virus. Even smallpox humbled us until the very end. That virus seemed to
have a better understanding of nature, human behavior, and ways to achieve
immortality than the entire smallpox eradication team. The emergence and
reemergence of infections must be approached with humility.
Enemies
Some anthropologists think conflict is not only inevitable but needed. Will
Durant once doubted the world could ever combine forces without fear of an
alien invasion. Perhaps disease could be used as a surrogate enemy?
Emerging infections are a powerful common enemy well suited as a global
challenge.
Focused Energy
Energy focused on a specific end can also build infrastructure. Energy
focused on eradication improved infrastructure. Surveillance, logistic
systems, evaluation, field teams, and cluster sampling are concepts used
during eradication that are now part of primary health care.
Optimism
The pessimists and cynics were not just wrong with smallpox; they were
harmful. They diverted attention, generated doubts in those who could
provide resources, invented problems far beyond the vast array of existing
ones. Even though negative news can be of value, their usefulness is
limited. Large problems should be approached with optimism.
Conclusions
Nine hundred years ago, building inventions converged and reached a peak,
leading builders and architects of the time to try ever bolder structures.
Cathedrals were built that in turn led to new innovations. For several
hundred years Europe was rewarded not only with cathedrals but also with
better building techniques for all structures. The infrastructure changed.
Historians, in a thousand years, will look on the public health cathedrals
that resulted from better building materials in a period of 75 years, from
the mid-20th century until the early 21st century. The control and
eradication of infectious diseases that once caused great trepidation
produced better diagnostic systems, treatment, and vaccines, the elements
with which to strengthen and improve the public health system and confront
new disease challenges.
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The Guinea Worm Eradication Effort: Lessons for the Future
Donald R. Hopkins
The Carter Center, Atlanta, Georgia, USA
------------------------------------------------------------------------
The dracunculiasis (Guinea worm) eradication campaign has specific
implications for efforts to control other emerging infectious diseases.
Guinea worm, a painful disfiguring disease, affects primarily adults, who
often become ill in very large numbers (usually 30% or more of a village's
population) during the planting or harvest season. The disease used to be
transmitted in parts of Asia and in Africa in open standing stagnant water.
The intermediate host of the parasite, the copepod, contains the larva of
the worm in such open drinking water; these organisms are barely visible in
a glass of drinking water held up to the light. Thirteen years ago, the
disease was still endemic in parts of the Indian subcontinent, a small part
of Pakistan and India, Yemen, and the band of countries across Africa from
east to west.
The Guinea Worm Eradication Campaign
Several interventions have been used to end transmission of Guinea worm
disease: health education (teaching people to filter their water through a
finely woven cloth and not to enter water when they or their neighbors are
infectious), safe drinking water from such sources as underground borehole
wells, and vector control (using Abate).
The Guinea worm campaign, like other campaigns in the past, has illustrated
the importance of political mobilization, including the mobilization of
national leaders. For example, General Amadou Toumani Touré (a charismatic
former head of state of the Republic of Mali), with the encouragement of
President Carter in 1992, made the eradication of Guinea worm disease in
Mali and in the nine other French-speaking countries in West Africa his
personal mission.
The campaign faces a problem common to many other efforts to control
infectious diseases in the industrialized and the developing world:
underreporting. For example, in Ghana, as in Nigeria 10 years ago, and in
many other countries, only three or four thousand cases of Guinea worm
disease were officially reported; but the actual numbers were much higher.
In 1989 when Ghana conducted a nationwide village-by-village search, almost
180,000 cases were found. Sudan began its eradication program late because
of civil war. In 1996 and 1997, an apparent decline of cases in Sudan was
due to less complete reporting because of increased fighting in 1997.
The Campaign's Implications for Other Diseases
The Guinea worm campaign has demonstrated very graphically the possibility
of village-based monthly reporting in Africa. In Ghana and Nigeria at the
beginning of this program 10 years ago, such reporting did not exist. Now
in those countries, more than 6,000 disease-endemic villages have
volunteers who report to the national capital monthly.
The Guinea worm campaign has also demonstrated very clearly the efficacy of
health education. In the beginning, many were skeptical because Guinea worm
could not be combated with a vaccine, and eradication efforts had to rely
on behavior change. However, behavior has changed. While we have been
successful in helping to bring safe drinking water to many disease-endemic
villages, the fastest and most effective intervention has been health
education, which helped people understand where the parasite was coming
from, how they were being infected, and the importance of using cloth
filters to protect themselves and their families.
The campaign has underscored the potential of local volunteers. Many years
ago in the Americas, village volunteers were used as part of malaria
control efforts. The onchocerciasis control program in Africa is also using
village volunteers successfully. The Guinea worm campaign has been another
illustration of how volunteers can be used to diagnose, report, and
provide, in this instance, on-the-spot treatment to neighbors for a
specific infection. Those responsible for the campaign's success are often
not members of the general health services.
With the help of the World Bank, the Guinea worm campaign demonstrates the
importance of disease eradication to the national economy. The World Bank
has estimated that the economic rate of return on the investment in Guinea
worm eradication will be on the order of 29% per year once the disease is
eradicated. That figure is based on a very conservative estimate of the
average amount of time infected workers are unable to perform agricultural
tasks.
The campaign has also created a group of trained health-care workers of a
different generation from those involved in the smallpox eradication
program. These workers have gone from beginning to end, from hearing the
doubters and seeing the difficulty of initiating the campaign to tasting
victory in their own countries. These workers can contribute to subsequent
campaigns. Moreover, the concept of eradication, which was in disrepute
only 5, 10 years ago, has been revived. Soon we will confirm that a
nonviral disease for which vaccine is not available can be eradicated.
Like the smallpox eradication campaign, the Guinea worm campaign has
illustrated very vividly in many different ways and at many different
levels (from international to village level) the power of data. In the
Guinea worm campaign, we have used surveillance data to promote health
policy. One key lesson from the smallpox campaign we are deliberately
applying in the Guinea worm campaign is to distill what needs to be done in
terms of interventions to a handful, or almost a handful, of indexes (seven
on an international level) to know what is most important and (as rapidly
as possible) how well we are doing. That unleashes inordinate amounts of
energy.
Finally, the Guinea worm eradication campaign will have illustrated again
the power of demonstration. Eradication can happen because it has happened.
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Nosocomial Infection Update
Robert A. Weinstein
Cook County Hospital & Rush Medical College, Chicago, Illinois, USA
---------------------------------------------------------------------------
Historically, staphylococci, pseudomonads, and Escherichia coli
have been the nosocomial infection troika; nosocomial
pneumonia, surgical wound infections, and vascular
access related bacteremia have caused the most illness and death
in hospitalized patients; and intensive care units have been
the epicenters of antibiotic resistance. Acquired antimicrobial
resistance is the major problem, and vancomycin-resistant
Staphylococcus aureus is the pathogen of greatest concern. The
shift to outpatient care is leaving the most vulnerable
patients in hospitals. Aging of our population and increasingly
aggressive medical and surgical interventions, including
implanted foreign bodies, organ transplantations, and
xenotransplantation, create a cohort of particularly
susceptible persons. Renovation of aging hospitals increases
risk of airborne fungal and other infections. To prevent and
control these emerging nosocomial infections, we need to
increase national surveillance, "risk adjust" infection rates
so that interhospital comparisons are valid, develop more
noninvasive infection-resistant devices, and work with
health-care workers on better implementation of existing
control measures such as hand washing.
As we enter the next millennium of infection control, we stand on the
shoulders of giants—Jenner, Semmelweis, Nightingale, Oliver Wendell Holmes,
and my own personal favorite, Thomas Crapper, the father of indoor
plumbing. Modern infection control is grounded in the work of Ignaz
Semmelweis, who in the 1840s demonstrated the importance of hand hygiene
for controlling transmission of infection in hospitals. However, infection
control efforts were spotty for almost a century. In 1976, the Joint
Commission on Accreditation of Healthcare Organizations published
accreditation standards for infection control, creating the impetus and
need for hospitals to provide administrative and financial support for
infection control programs. In 1985, the Centers for Disease Control and
Prevention's (CDC's) Study on the Efficacy of Nosocomial Infection Control
reported that hospitals with four key infection control components—an
effective hospital epidemiologist, one infection control practitioner for
every 250 beds, active surveillance mechanisms, and ongoing control
efforts—reduced nosocomial infection rates by approximately one third (1).
Over the past 25 years, CDC's National Nosocomial Infections Surveillance
(NNIS) system has received monthly reports of nosocomial infections from a
nonrandom sample of United States hospitals; more than 270 institutions
report. The nosocomial infection rate has remained remarkably stable
(approximately five to six hospital-acquired infections per 100
admissions); however, because of progressively shorter inpatient stays over
the last 20 years, the rate of nosocomial infections per 1,000 patient days
has actually increased 36%, from 7.2 in 1975 to 9.8 in 1995 (Table 1). It
is estimated that in 1995, nosocomial infections cost $4.5 billion and
contributed to more than 88,000 deaths—one death every 6 minutes.
Table 1. Nosocomial infections, United States (2,3)
-----------------------------------------------------------------
Nosoco-
mial
Nosoco- infections
Admis- Patient Length mial (/1000
sions days(sup a) of stay infection patient
Year (x106) (x106) (days) (x106) days)
----------------------------------------------------------------
1975 38 299 7.9 2.1 7.2
1995 36 190 5.3 1.9 9.8
------------------------------------------------------------------
(sup a)Patient days = total inpatient days
Which Nosocomial Infections Are Emerging?
We have witnessed a cyclical parade of pathogens in hospitals. In Semmelweis's
era, group A streptococci created most nosocomial problems. For the next 50 to
60 years, gram-positive cocci, particularly streptococci and Staphylococcus
aureus, were the hospital pathogens of major concern. These problems
culminated in the pandemic of 1940 to 1950, when S. aureus phage type 94/96
caused major nosocomial problems. In the 1970s, gram-negative bacilli,
particularly Pseudomonas aeruginosa and Enterobacteriaceae, became
synonymous with nosocomial infection. By the late 1980s and early 1990s,
several different classes of antimicrobial drugs effective against gram-negative
bacilli provided a brief respite. During this time, methicillin-resistant S. aureus
(MRSA) and vancomycin-resistant enterococci (VRE) emerged, signaling the
return of the "blue bugs." In 1990 to 1996, the three most common
gram-positive pathogens—S. aureus, coagulase-negative staphylococci, and
enterococci—accounted for 34% of nosocomial infections, and the four most
common gram-negative pathogens—Escherichia coli, P. aeruginosa, Enterobacter
spp., and Klebsiella pneumoniae—accounted for 32% (3).
Bloodstream infections and pneumonias have increased in frequency from 1975
to 1996 (Table 2). However, tracking nosocomial infections by site has
become difficult in the last few years because of shorter inpatient stays.
For example, the average postoperative stay, now approximately 5 days, is
usually shorter than the 5- to 7-day incubation period for S. aureus
surgical wound infections.
Table 2. Sites of nosocomial infections (2,4)
-------------------------------------------------------
Lower
respira-
Urinary Surgical tory Blood-
tract wound tract stream Other
Year (%) (%) (%) (%) (%)
--------------------------------------------------------
1975 42 24 10 5 19
1990-6 34 17 13 14 21
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Acquired antimicrobial resistance is the major anticipated problem in hospitals.
VRE and MRSA are the major gram-positive pathogens of concern (5,6). P.
aeruginosa, Klebsiella, and Enterobacter that harbor chromosomal or
plasmid-mediated beta-lactamase enzymes are the major resistant
gram-negative pathogens. The contribution of antibiotic resistance to excessive
death rates in hospitals is difficult to evaluate, often depending on whether
studies are population-based or case-control, but evidence is mounting that
antimicrobial resistance contributes to nosocomial deaths.
While bacterial resistance is clearly the major threat, viral and fungal
resistance could become important because of the small number of
therapeutic options for these pathogens. Herpes viruses with acquired
resistance to acyclovir and ganciclovir have emerged as problems,
particularly in HIV-infected patients. Pathogens with intrinsic resistance
often have lower pathogenicity and have disproportionately affected
immunocompromised patients. For example, Candida spp. with intrinsic
resistance to azole antifungal agents (e.g., C. krusei) and to amphotericin
B (e.g., C. lusitaniae) have emerged as problem pathogens in oncology
units.
While we are facing the era of opportunists, including fungi, viruses, and
parasites in immunocompromised patients, the one we fear most is the
postantibiotic era. The first nosocomial inkling is MRSA with reduced
susceptibility to vancomycin (7). Beyond the postantibiotic era lies the
era of xenogenic infections as organs, transplanted from nonhuman primates,
bring with them a variety of potential zoonotic pathogens. Nevertheless,
traditional respiratory pathogens may yet prove to be our greatest
challenge; for example, a major shift in strain type (8) could result in
devastating pandemic community and nosocomial influenza A outbreaks.
Who Is Affected by Emerging Nosocomial Pathogens?
Nosocomial infections typically affect patients who are immunocompromised
because of age, underlying diseases, or medical or surgical treatments.
Aging of our population and increasingly aggressive medical and therapeutic
interventions, including implanted foreign bodies, organ transplantations,
and xenotransplantations, have created a cohort of particularly vulnerable
persons. As a result, the highest infection rates are in intensive care
unit (ICU) patients. Nosocomial infection rates in adult and pediatric ICUs
are approximately three times higher than elsewhere in hospitals. The sites
of infection and the pathogens involved are directly related to treatment
in ICUs. In these areas, patients with invasive vascular catheters and
monitoring devices have more bloodstream infections due to
coagulase-negative staphylococci. In fact, most cases of occult bacteremia
in ICU patients are probably due to vascular access-related infections.
Fungal urinary tract infections have also increased in ICU patients,
presumably because of extensive exposure to broad-spectrum antibiotics. In
the National Nosocomial Infections Surveillance system, Candida spp. are
the main cause of nosocomial urinary infections in ICUs (9).
Why Are Nosocomial Infections Emerging Now?
Three major forces are involved in nosocomial infections. The first is
antimicrobial use in hospitals and long-term care facilities. The increased
concern about gram-negative bacilli infections in the 1970s to 1980s led to
increased use of cephalosporin antibiotics. As gram-negative bacilli became
resistant to earlier generations of cephalosporin antibiotics, newer
generations were developed. Widespread use of cephalosporin antibiotics is
often cited as a cause of the emergence of enterococci as nosocomial
pathogens. About the same time, MRSA, perhaps also in response to extensive
use of cephalosporin antibiotics, became a major nosocomial threat.
Widespread empiric use of vancomycin, as a response to concerns about MRSA
and for treatment of vascular catheter-associated infection by resistant
coagulase-negative staphylococci, is the major initial selective pressure
for VRE. Use of antimicrobial drugs in long-term care facilities and
transfer of patients between these facilities and hospitals have created a
large reservoir of resistant strains in nursing homes.
Second, many hospital personnel fail to follow basic infection control,
such as hand washing between patient contacts. In ICUs, asepsis is often
overlooked in the rush of crisis care (10).
Third, patients in hospitals are increasingly immunocompromised. The shift
of surgical care to outpatient centers leaves the sickest patients in
hospitals, which are becoming more like large ICUs (11). This shift has led
to the greater prevalence of vascular access associated bloodstream
infections and ventilator-associated pneumonias.
Other precipitating factors also can be anticipated in hospitals.
Transplantation is a double-edged sword because of the combined effects of
immunosuppression of transplant patients and of infectious diseases that
come with some transplanted organs. The blood supply will continue to be a
source of emerging infectious diseases. Moreover, as hospitals age,
infrastructure repairs and renovations will create risks of airborne fungal
diseases caused by dust and spores released during demolition and
construction. Infections due to other pathogens, such as Legionella, may
also result from such disruptions.
How Can We Prevent and Control Emerging Nosocomial Infections?
Infection control can be very cost-effective. Approximately one third of
nosocomial infections are preventable. To meet and exceed this level of
prevention, we need to pursue several strategies simultaneously (12).
First, we need to continue to improve national surveillance of nosocomial
infections so that we have more representative data. We must assess the
sensitivity and specificity of our surveillance and of our case
definitions, particularly for difficult-to-diagnose infections like
ventilator-associated pneumonia. We also need to develop systems for
surveillance of "nosocomial" infections that occur out of the hospital,
where much health care is now given.
Second, we need to ensure that surveillance uses are valid. The Joint
Commission on Accreditation of Healthcare Organization's ORYX initiative
for monitoring health-care processes and outcomes will lead to core
indicators and sentinel event monitoring. This initiative will be followed
by increased outpatient surveillance, which ultimately may lead to
systemwide real-time surveillance and reporting. Because we want to use
nosocomial infection rates as a core indicator of quality of care, we need
to improve our ability to "risk adjust" infection rates so we know that our
interprovider and interhospital comparisons are valid. Risk stratification
will ultimately depend on organic-based computer systems that will mimic
biologic events.
Third, many of our successes in controlling nosocomial infections have come
from improving the design of invasive devices. This is particularly
important given the marked increase in frequency of vascular
access associated bloodstream infections, particularly in ICU patients.
Given the choice of changing human behavior (e.g., improving aseptic
technique) or designing a better device, the device will always be more
successful. Of particular importance is the development of noninvasive
monitoring devices and minimally invasive surgical techniques that avoid
the high risk associated with bypassing normal host defense barriers (e.g.,
the skin and mucous membranes).
Fourth, forestalling the postantibiotic era will require aggressive
antibiotic control programs (13); these may become mandated for hospitals
that receive federal reimbursements, as happened in the past with infection
control programs. Risks for antibiotic-resistant strains also may be
reduced in the future by controlling colonization through use of
immunization or competing flora.
Fifth, antimicrobial resistance problems and the advent of
xenotransplantation emphasize the importance of newer microbiologic
methods. For investigation of outbreaks of multidrug-resistant pathogens,
pulsed-field gel electrophoresis has become a routine epidemiologic tool
(14). Molecular epidemiologic analysis also may help us better understand
the factors that lead to the emergence of resistant strains. For diagnosis
of syndromes caused by unusual pathogens, representational difference
analysis and speciation by use of the pathogen's phylogenetic r-RNA "clock"
may become routine.
Sixth, control of tuberculosis (TB) in hospitals is an excellent example of
the successful collaboration of the infection control community, CDC, and
regulatory agencies. But we can anticipate that the Occupational Safety and
Health Administration may have many new employee health issues beyond TB
and bloodborne pathogens to evaluate in hospitals, such as health problems
related to exposure to magnetic fields, to new polymers, and to medications
that contaminate the environment. Problems of mental stress due to
unrelenting exposure to pagers, faxes, e-mail, holograms, and telephonic
implanted communicators will require special attention.
Conclusion
Several enduring truths characterize the field of infection control.
Hospitals will become more like ICUs, and more routine care will be
delivered on an outpatient basis. Given the choice of improving technology
or improving human behavior, technology is the better choice. All infection
control measures will need to continue to pass the test of the "four Ps"
(15): Are the recommendations Plausible biologically (e.g., is it likely to
work)? Are they Practical (e.g., are they affordable)? Are they Politically
acceptable (e.g., will the administration agree)? And, will Personnel
follow them (e.g., can they and will they)?
The major advances in overall control of infectious diseases have resulted
from immunization and improved hygiene, particularly hand washing. We must
work with hospital personnel on better implementation of existing infection
control technologies so that we will not need to rely solely on technologic
advances.
Dr. Weinstein is chair, Division of Infectious Diseases, Cook County
Hospital; director of Infectious Diseases Services for the Cook County
Bureau of Health Services; and professor of Medicine, Rush Medical College.
He also oversees the CORE Center for the Prevention, Care and Research of
Infectious Disease and directs the Cook County Hospital component of the
Rush/Cook County Infectious Disease Fellowship Program. His areas of
research include nosocomial infections (particularly the epidemiology and
control of antimicrobial resistance and infections in intensive care units)
and health-care outcomes for patients with HIV/AIDS.
References
1. Haley RW, Culver DH, White J, Morgan WM, Amber TG, Mann VP, et al.
The efficacy of infection surveillance and control programs in
preventing nosocomial infections in US hospitals. Am J Epidemiol
1985;121:182-205.
2. Haley RW, Culver DH, White JW, Morgan WM, Emori TG. The nationwide
nosocomial infection rate: a new need for vital statistics. Am J
Epidemiol 1985;121:159-67.
3. New York Times 1998 Mar 12; Sect. A12.
4. Centers for Disease Control and Prevention, Hospital Infections
Program. National Nosocomial Infections Surveillance (NNIS) report,
data summary from October 1986-April 1996, issued May 1996: A report
from the NNIS System. Am J Infect Control 1996;24:380-8.
5. Slaughter S, Hayden MK, Nathan C, Hu TC, Rice T, Van Voorhis J, et al.
A comparison of the effect of universal use of gloves and gowns with
that of glove use alone on acquisition of vancomycin-resistant
enterococci in a medical intensive care unit. Ann Intern Med
1996;125:448-56.
6. Bonten MJM, Hayden MK, Nathan C, Van Voorhis J, Matushek M,
Slaughter S, et al. Epidemiology of colonisation of patients and
environment with vancomycin-resistant enterococci. Lancet 1996;348:1615-9.
7. Hiramatsu K, Aritaka N, Hanaki H, Kawasaki S, Hosoda Y, Hori S, et al.
Dissemination in Japanese hospitals of strains of Staphylococcus
aureus heterogeneously resistant to vancomycin. Lancet
1997;350:1670-3.
8. Webster RG. Influenza: an emerging disease. Emerg Infect Dis
1998;4(3).
9. Fridkin SK, Welbel SF, Weinstein RA. Magnitude and prevention of
nosocomial infections in the intensive care unit. Infect Dis Clin
North Am 1997;11:479-96.
10. Weinstein RA. Epidemiology and control of nosocomial infections in
adult intensive care units. Am J Med 1991;91:179-84.
11. Archibald L, Phillips L, Monnet D, McGowan JE, Tenover F, Gaynes R.
Antimicrobial resistance in isolates from inpatients and outpatients
in the United States: increasing importance of the intensive care
unit. Clin Infect Dis 1997;24:211-5.
12. Scheckler WE, Brimhall D, Buck AS, Farr BM, Friedman C, Garibaldi RA,
et al. Requirements for infrastructure and essential activities of
infection control and epidemiology in hospitals: a consensus panel
report. Infect Control Hosp Epidemiol 1998;19:114-24.
13. Goldmann DA, Weinstein RA, Wenzel RP, Tablan OC, Duma RJ, Gaynes
RP, et al. Strategies to prevent and control the emergence and spread of
antimicrobial-resistant microorganisms in hospitals. A challenge to
hospital leadership. JAMA 1996;275:234-40.
14. Tenover FC, Arbeit RD, Goering RV. How to select and interpret
molecular strain typing methods for epidemiological studies of
bacterial infections: a review for healthcare epidemiologists. Infect
Control Hosp Epidemiol 1997;18:426-39.
15. Weinstein RA. SHEA consensus panel report: a smooth takeoff. Infect
Control Hosp Epidemiol 1998;19:91-3.
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Opportunistic Infections in Immunodeficient Populations
Jonathan E. Kaplan,* Gary Roselle,† and Kent Sepkowitz‡
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA;
†Veterans Administration Medical Center, Cincinnati, Ohio, USA; and
‡Memorial Sloan-Kettering Cancer Center, New York, New York, USA
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Opportunistic infections occur with greater frequency or severity in
patients with impaired host defenses. Growing numbers of HIV-infected
persons, transplant recipients, and elderly persons are at increased risk.
Alison Grant, London School of Hygiene and Tropical Medicine, discussed
opportunistic infections due to HIV. In 1997, more than 30 million
HIV-infected persons lived in the world, with more than two thirds of them
in sub-Saharan Africa and an additional 20% in Asia and Latin America.
Assessments of the prevalence and incidence of opportunistic infections in
these areas and comparability of the available data are hampered by limited
access to care, diagnostic capabilities, and surveillance data. Despite
these limitations, we know that tuberculosis (TB) is the most frequent
serious opportunistic infection in the developing world. Other such
infections common in sub-Saharan Africa include septicemia (of which
nontyphoid salmonella is the most common cause), toxoplasmosis, and
bacterial pneumonia. Pneumocystis carinii infection, for unknown reasons,
is uncommon among adults in East and West Africa but appears to be more
common in South Africa. Penicillium marneffei infection, common in
Thailand, is an example of an opportunistic infection of importance in a
specific region; risk factors in these regions are largely unknown.
Additional challenges are posed by the different HIV subtypes in the
developing world and the possibility that some may be associated with a
differential risk for opportunistic infections. Prevention efforts in
developing countries have been limited. More work is needed to evaluate
prophylactic regimens appropriate to different regions. Prevention of TB
with isoniazid; of pneumocystosis, toxoplasmosis, and some bacterial
infections with cotrimoxazole; and of pneumococcal infections with
23-valent pneumococcal vaccine have potential.
Robert Hogg, University of British Columbia, discussed the remarkable
changes in the natural history of HIV in North America, specifically in
British Columbia, as a result of highly active antiretroviral therapy
(HAART). Of more than 5,000 HIV-infected persons receiving care in British
Columbia, more than 2,000 are receiving HAART. HIV viral loads have been
reduced to undetectable levels in approximately half of these patients,
with corresponding decreases in the incidence of opportunistic infections,
hospitalizations, and deaths. However, even for persons who have access to
the therapy, these successes may be short-lived as resistance to HAART
becomes more widespread. HAART use has resulted in new syndromes that may
occur soon after therapy, probably representing preexisting, subclinical
infections that are unmasked by the immunologic improvement that
accompanies HAART; these syndromes include lymphadenitis associated with
Mycobacterium avium complex, cytomegalovirus retinitis, and miliary TB on
chest X-ray. Hepatitis C infection, common in HIV-infected injection drug
users, may pose increasing problems as coinfected persons live longer.
Therefore, surveillance for old and new syndromes remains critical even
with the reduced incidence of opportunistic infections that has been
associated with HAART.
Robert Rubin, Harvard University and Massachusetts Institute of Technology,
discussed opportunistic infections in hematopoietic stem cell (bone marrow)
and solid-organ transplant recipients; the number of these transplant
recipients has increased dramatically in the United States in the past
decade. The opportunistic infections in these patients originate from
endogenous flora (e.g, invasive candidiasis), from the general
(nonhospital) environment (e.g, histoplasmosis, TB, disseminated
strongyloidiasis), or from the hospital environment (e.g, aspergillosis,
legionellosis, and infections with vancomycin-resistant enterococci or
multiply resistant gram-negative bacteria). These infections
characteristically occur in a time-dependent pattern posttransplant,
corresponding with the nature of the immunodeficiency. For example, in bone
marrow transplant recipients, infections within 1 month of transplantation
(pre-engraftment) occur as a result of neutropenia and disruption of
mucosal surfaces; infections that occur in the second or third months are
due to deficiencies in cell-mediated immunity and are more frequent in the
setting of graft versus host disease. In solid-organ transplant recipients,
infections within the first month are generally associated with technical
problems related to surgery; infections that occur later are due to
immunodeficiency associated with immunosuppressive therapy. These
timetables are useful in that infections that are unusual or occur outside
the expected time frame may serve as sentinels for emerging opportunistic
infections. Research priorities in this area include development of
therapies that will enhance successful transplantation without increasing
the risk for opportunistic infections, strategies to reduce the risk of
drug-resistant opportunistic infections, and greater understanding of the
role of cytokines in the relationship between graft versus host disease and
opportunistic infections.
Carol Kauffman, University of Michigan and the Ann Arbor Veterans
Administration Medical Center, discussed infections in the elderly, a
population that is increasing in the United States and worldwide. Persons
>65 years of age already constitute approximately one eighth of the U.S.
population; this proportion is expected to double in the next 50 years.
Elderly persons have defects in T-cell immunity that result in increased
incidence and death from TB. B-cell defects result in increased
susceptibility to Streptococcus pneumoniae and respiratory syncytial virus
and a decreased response to 23-valent pneumococcal vaccine. Elderly persons
are at increased risk for cancer, so various treatments associated with
immunosuppression (such as organ transplantation and aggressive cancer
chemotherapy) are increasingly being used in this population. Chronic
corticosteroid therapy is frequently used for treatment of temporal
arteritis. Although HIV infection is relatively uncommon in the elderly,
when it does occur, it is likely to go undiagnosed. Because of higher rates
of hospitalization, elderly persons are more susceptible to nosocomial
infections (including those caused by antibiotic-resistant organisms).
Moreover, the elderly are more likely to reside in long-term care
facilities, which may serve as sources or amplifiers of infections such as
influenza. Susceptibility to infection may be further increased by
malnutrition, diabetes, and chronic renal failure. Finally, healthy, more
affluent older persons are at risk for infections associated with travel.
In summary, opportunistic infections are a threat in the increasing
populations of immunocompromised persons. In these populations,
opportunistic infections pose challenges for surveillance and determination
of risk factors, including those for infection with antibiotic-resistant
organisms.
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Host Genes and Infectious Diseases
Janet McNicholl
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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This panel presented data on host genes that influence susceptibility to or
manifestations of four infectious diseases: Puumala hantavirus infection,
tuberculosis (TB), Lyme disease, and AIDS. Gus Birkhead, Council of State
and Territorial Epidemiologists, introduced the session, highlighting its
timeliness in relation to the rapidly emerging body of data on our 100,000
human genes that stems from the Human Genome and related projects.
The presentations introduced several approaches to identifying a host
gene-infectious disease interaction. Panelists presented case-control
studies of hantavirus infection, AIDS, TB, and Lyme disease that used the
candidate gene approach; the new approach, genome scanning by
microsatellites to identify genes associated with TB susceptibility, was
also described. Candidate genes were chosen on the basis of pathology of
the infectious disease (human leukocyte antigen [HLA], tumor necrosis
factor [TNF], the antigen processing [TAP]), mouse genetic studies of the
pathogen (NRAMP1 in TB), or epidemiologic findings of disease severity
(Vitamin D and TB).
Susceptibility-Associated Major Histocompatibility Complex (MHC) Haplotype
in Severe Puumala Hantavirus Infection
Annti Vaheri, Haartman Institute, University of Helsinki, described the
epidemiology of hantavirus infections in Northern Europe. The pathogens,
enveloped RNA viruses primarily of the Puumala and Dobrava genotypes, are
carried by rodents such as mice and voles and cause a range of disease in
humans. While the epidemics in the United States are of hantaviruses that
cause primarily pulmonary disease, in northern Europe, renal disease is the
primary pathologic manifestation, as evidenced by increased capillary
permeability, infiltrates of CD8+ T cells, high levels of ICAM-1, and
expression of TNF-alpha and transforming growth factor (TGF)-ß. Although most
infections with these viruses are probably subclinical or cause mild
disease, in 10% of patients disease may progress to shock, 5% may require
dialysis, and some may die. Of those who recover, renal damage may later
result in chronic hypertension. Because hantaviruses are variable and are
usually transmitted as swarms of viruses, it was proposed that host
factors, such as HLA genes, might influence the spectrum of disease.
Indeed, this has been shown to be the case. Persons who express the HLA-B8
genes had more severe disease with lower blood pressures, higher creatinine
(1), and more virus in the urine and blood by polymerase chain reaction
(PCR) (2). Persons with HLA-B27 had milder disease (3). The finding of
TNF-alpha expression in the kidney of infected patients prompted an analysis of
the TNF 1 and 2 alleles (at positions -308 and -238) by restriction
fragment length polymorphism (RFLP), and as might have been predicted from
their linkage to the HLA-A1-B8-DR3 haplotype, nearly all who progressed to
shock expressed the TNF 2 allele (M. Kanerva, unpub. data). This allele has
been linked to high TNF production (4).
Because the HLA-A1-B8-DR3 MHC haplotype is associated with
insulin-dependent diabetes mellitus and other autoimmune diseases that may
have a viral etiology, it was asked if molecular mimicry could explain the
association of this haplotype with the renal disease of Puumala virus
infection. Dr. Vaheri stated that no such evidence exists and that the
association probably reflects a propensity to a particular type of immune
response that results in disease. Whether the genetic associations observed
with Puumala hantavirus disease are due to a primary association with the
TNF 2 allele or the linked HLA alleles is not known and deserves future
research. Another important field is the mapping of HLA-restricted epitopes
in hantaviruses.
Host Susceptibility to TB in Africa
Although TB has been present in human populations for millennia, its
reemergence as a public health problem and the new tools of molecular
genetics have provided an impetus to study host genetic susceptibility to
TB disease. Richard Bellamy, Wellcome Trust Center for Human Genetics,
presented studies that used both candidate- and genome-screening approaches
to define these factors in African populations. As stated during the
question-and-answer session, many studies of TB should be considered
studies of TB disease rather than TB susceptibility, since most persons,
particularly in Africa, are TB infected, but (at least in HIV-negative
populations) fewer than 10% become ill. Dr. Bellamy's studies were carried
out in populations with low HIV prevalence, HIV-infected persons were
excluded, and disease was defined as smear-positive TB. Historically, in
most populations, particularly in The Gambia and South Africa, the sources
of patients and controls for these studies, TB is predominantly a disease
of males. Previous studies of mono- and dizygotic twins have also suggested
a genetic component (reviewed in 5).
One of the studies described by Dr. Bellamy used new tools from the human
genome and other projects called microsatellite markers (intronic sections
of cytosine, adenine repeats) and automated robotic DNA typing using
four-color fluorescent labels with 20 markers per lane of large gels that
are scanned and analyzed by software such as GeneScan 672 and Genotyper
1.2. He analyzed 92 sibling-pairs from The Gambia and South Africa.
Cosegregation with TB was identified for markers on chromosomes 3, 5, 6, 8,
9, 15, and the X chromosome. A second study of 83 sibling-pairs from the
same countries again linked the same sites on Xq and 15p with lod scores of
>2. While these studies do not identify the genes in question, further
studies of these regions may reveal the relevant genes (e.g., the
microsatellite region identified on Xq is close to genes encoding the CD40
ligand and human LAMP).
Bellamy's group identified two additional genes associated with TB in
candidate gene association studies of African TB cases and ethnically
matched controls (6). The human homologue NRAMP1 of the mouse Bcg gene that
confers resistance to bacillus Calmette-Guérin has been located on
chromosome 2q35. Four polymorphisms in NRAMP1 were studied with
microsatellite markers and probes that distinguished single-base
substitutions and a 4-bp deletion in the gene. While all four polymorphisms
were associated with TB, two, one intronic and another in the 3'
untranslated region, were particularly overrepresented in TB patients;
persons heterozygous for INT4 GC and 3'UTR deletion had a fourfold
increased risk of having TB (6). The 3'UTR allele is of unusually high
prevalence in the West African population studies but is uncommon in
Europeans. This may partly explain the higher susceptibility to TB in
African Americans compared with other ethnic groups. While the physiologic
function of NRAMP1 has not been defined, it may affect phagolysosome
function. Dr. Bellamy's data suggest that the polymorphisms they have
defined or linked polymorphisms may alter NRAMP1 function and therefore the
host's ability to clear intracellular pathogens. In vitro studies to
address the effect of these polymorphisms on macrophage function are in
progress.
Dr. Bellamy also presented unpublished data on vitamin D receptor genotypes
and susceptibility to TB disease. This gene was chosen because of clinical
and laboratory data suggesting vitamin D may be important in host defenses
against TB (7,8). He observed a low prevalence of the homozygous t vitamin
D receptor genotype in TB cases but not in controls. This genotype is also
associated with increased risk for osteoporosis (9,10). These findings
raise the question whether administering vitamin D to populations at risk
for TB disease might be a simple public health measure to reduce the
disease. However, the effect of such therapy might be hard to estimate
because of the low prevalence of the tt homozygous genotype.
The genes (e.g., HLA) identified in these and other studies are certainly
not the only genes involved in host susceptibility to TB. Dr. Bellamy
estimated that together they account for less than 2% of the total familial
clustering effect in this disease.
HLA and the Pathogenesis of Lyme Arthritis
Host responses to another bacterium, the spirochete Borrelia burgdorferi,
and the clinical spectrum of Lyme arthritis were discussed by Allen Steere,
Department of Rheumatology and Immunology, New England Medical Center,
Boston, Massachusetts. Another vector-borne human pathogen, B. burgdorferi
causes a multisystem disease that may affect the skin, nervous system,
heart, or joints. Arthritis is a major late manifestation of the illness.
Although all manifestations are usually treatable with antibiotic therapy,
approximately 10% of patients with Lyme arthritis have persistent joint
inflammation for months or even years after antibiotic therapy. In these
patients, PCR tests for B. burgdorferi DNA in joint fluid have been
negative after antibiotic treatment, which suggests that joint inflammation
may sometimes continue after the spirochete has been eradicated from the
joint.
Dr. Steere's group is studying host factors that may be important in the
pathogenesis of chronic, treatment-resistant Lyme arthritis. Studies of HLA
class II alleles have shown that HLA-DRB1*0401 alleles are associated with
chronic Lyme arthritis and lack of response to antibiotic therapy (11).
This allele is also associated with an increased risk of developing severe
rheumatoid arthritis (12). In a study of antibody responses in patients
throughout the course of Lyme disease, immunoglobulin G (IgG) responses to
outer-surface protein A (OspA) and OspB of the spirochete often developed
near the beginning of prolonged episodes of arthritis (13). Arthritis
lasted considerably longer after treatment in patients with HLA-DR4 and
OspA and OspB antibody reactivity than in those who lacked responses to
these proteins (13). The cellular arm of the immune response has also been
examined by Dr. Steere's group, and persons with treatment-resistant Lyme
arthritis usually have T cells that react with many OspA epitopes, whereas
treatment-responsive patients usually do not. A possible explanation for
these findings is that the T-cell response to OspA in patients with
treatment-resistant Lyme arthritis may cross-react with a self antigen in
the joint, and the response to this self antigen may continue to cause
joint inflammation for months or even years after the eradication of the
spirochete from the joint.
How does one treat patients with Lyme arthritis who do not appear to
respond to therapy? Dr. Steere recommended that if they have not responded
to antibiotics after 2 months and the PCR test on joint fluid is negative
for B. burgdorferi DNA, patients should be treated with antiinflammatory
agents. When asked whether HLA genes might influence Osp-based vaccines for
Lyme disease, Dr. Steere noted that studies to address this question have
not yet been carried out.
Host Genes, HIV Susceptibility, and Disease Course
The rapidly growing and complex body of knowledge on the host genes that
influence susceptibility to HIV infection and progression to AIDS was
reviewed by Richard Kaslow, Department of Epidemiology, University of
Alabama, Birmingham, Alabama. The studies reported by Kaslow and others in
the last 2 years have greatly benefited from several longitudinal cohort
studies, some focusing on HIV-infected seroconverters or HIV-exposed
persons in the United States and Europe. More than 10 years after these
cohorts have been established, adequate power to address the role of
candidate genes in transmitting HIV horizontally and vertically and in
affecting the rate of disease progression has been obtained, while
increased knowledge of HIV's mode of cellular entry has provided new
candidate genes to study. HIV enters cells through an interaction with both
CD4 and a chemokine receptor of the 7 Tm family (14). Dr. Kaslow first
reviewed the role of genes in encoding chemokine receptors (CCR5 and CCR2)
and chemokines (SDF-1) in HIV disease. While CCR5 has multiple allelic
variants in its coding region (15), the deletion of a 32-bp segment results
in a nonfunctional receptor (reviewed in 16), thus preventing HIV entry;
two copies of this gene provide strong protection against HIV infection in
epidemiologic studies, although the protection is not absolute. This gene
is found in up to 20% of Europeans but is rare in Africans and Asians.
Multiple studies of HIV-infected persons have shown that presence of one
copy of this gene delays progression to AIDS by about 2 years. A mutation
in another chemokine receptor gene, that coding for CCR2, has also been
reported by several groups to be associated with a delayed progression to
AIDS (reviewed in 17). This polymorphism (a position 64 Val -> Ile
substitution) does not appear likely to affect receptor function, and the
mutation may be linked to another polymorphism in the promotor of CCR5
(18). Nevertheless, studies of persons with both CCR2 64I polymorphism and
CCR5 delta 32 deletion suggest the effect of both genes on HIV disease
progression is additive (19). A polymorphism in the chemokine SDF-1, which
binds to another HIV entry receptor, CXCR4, also delays HIV progression and
similarly appears additive to the effects of the CCR2 and CCR5
polymorphisms (20).
Dr. Kaslow also reviewed studies of the HLA system (at the Class I HLA A,
B, C and Class II DR and DQ and the antigen processing [TAP] loci) and how
complex combinations of different HLA alleles alter the risk of developing
AIDS in several cohorts of HIV-infected persons (20). The effects of
different combinations of HLA alleles appear to delay HIV progression by a
variable number of years and to be additive to the effects of the chemokine
gene polymorphisms described above.
These new findings about HIV and host genes have led to new approaches to
AIDS treatments, such as those directed at chemokine receptors, and hold
great promise for advancing our ability to combat this disease.
References
1. Mustonen J, Partanen J, Kanerva M, Pietilä K, Vapalahti O, Pasternack
A, et al. Genetic susceptibility to severe course of nephropathia
epidemica caused by Puumala hantavirus. Kidney Int 1996;49:217-21.
2. Plyusnin A, Hörling J, Kanerva M, Mustonen J, Cheng Y, Partanen J, et
al. Puumala hantavirus genome in patients with nephropathia epidemica:
correlation of PCR positivity with HLA haplotype and link to viral
sequences in local rodents. J Clin Microbiol 1997;35:1090-6.
3. Mustonen J, Partanen J, Kanerva M, Pietilä K, Vapalahti O, Pasternack
A, et al. Asssociation of HLA B27 with benign clinical course of
nephropathia epidemica caused by Puumala hantavirus. Scand J Immunol.
In press 1998.
4. Wilson AG, Symons JA, McDowell TL, McDevit HO, Duff GW. Effects of
polymorphism in the tumor necrosis factor alpha promoter on
transcriptional activation. Proc Natl Acad Sci U S A 1997;94:3195-9.
5. Bloom BR, Small PM. Editorial. The evolving relation between humans
and Mycobacterium tuberculosis. N Engl J Med 1998;338:677-8.
6. Bellamy R, Ruwende C, Tumani C, McAdam PWJ, Whittle HC, Hill AVS.
Variations in the NRAMP1 gene and susceptibility to tuberculosis in
West Africans. N Engl J Med 1998;338:640-4.
7. Davies PD. A possible link between vitamin D deficiency and impaired
host defence to Mycobacterium tuberculosis. Tubercle 1985;66:301-6.
8. Rook GA, Steele J, Fraher L, Barker S, Karmali R, O'Riordan J, et al.
Vitamin D3, gamma interferon, and control of proliferation of
Mycobacterium tuberculosis by human monocytes. Immunology.
1986;57:159-63.
9. Sainz J, Van Tornout JM, Loro ML, Sayre J, Roe TF, Gilsanz V. Vitamin
D–receptor gene polymorphisms and bone density in prepubertal American
girls of Mexican descent. N Engl J Med. 1997;337(2):7782.
10. Morrison NA, Qi JC, Tokita A, Kelly PJ, Crofts L, Nguyen TV, et al.
Prediction of bone density from vitamin D receptor alleles. Nature
1994;367(6460):284287.
11. Steere AC, Dwyer E, Winchester R. Association of chronic Lyme
arthritis with HLA-DR4 and HLA-DR2 alleles. N Engl J Med
1990;323:219-23.
12. Gregerson PK, Silber J, Winchester RJ. The shared epitope hypothesis:
an approach to understanding the molecular genetics of rheumatoid
arthritis. Arthritis Rheum 1987;30:1205-13.
13. Kalish RA, Leong JM, Steere AC. Association of treatment-resistant
chronic Lyme arthritis with HLA-DR4 and antibody reactivity with OspA
and OspB of Borrelia burgdorferi. Infect Immun 1993;61:2774-9.
14. Murphy PM. Chemokine receptors: structure, function and role in
microbial pathogenesis. Cytokine & Growth Factor Reviews 1996;7:47-64.
15. Carrington M, Kissner T, Gerrard B, Ivanov S, O'Brien SJ, Dean M.
Novel alleles of the chemokine-receptor gene CCR5. Am J Hum Genet
1997;61:1261-7.
16. McNicholl JM, Smith DK, Qari SH, Hodge T. Host genes and HIV: the role
of the chemokine receptor gene CCR5 and its allele (delta32 CCR5). Emerg
Infect Dis 1997:3:261-71.
17. Garred P. Chemokine-receptor polymorphisms: clarity or confusion for
HIV prognosis [editorial]. Lancet 1998;351:2-3.
18. Kostrikis LG, Huang Y, Moore JP, Wolinsky SM, Zhang L, Guo Y, et al. A
chemokine receptor CCR2 allele delays HIV progression and is
associated with a CCR5 promotor mutation. Nature Med 1998;4;350-3.
19. Smith MW, Dean M, Carrington M, Winkler C, Huttley GA, Lomb DA, et al.
Contrasting genetic influence of CCR 2 and CCR5 variants on HIV
infection and disease progression. Science 1997;277;959-65.
20. Winkler C, Modi W, Smith MW, Nelson GW, Wu X, Carrington M, et al.
Genetic restriction of AIDS pathogenesis by an SDF-1 chemokine gene
variant. Science 1998;279;380-93.
21. Kaslow RA, Carrington M, Apple R, Park L, Munoz A, Saah AJ, et al.
Influence of combinations of human major histocompatibility complex
genes on the course of HIV-1 infection. Nature Medicine 1996;2:405-11.
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Immigrant and Refugee Health
Susan Cookson,* Ronald Waldman,* Brian Gushulak,† Douglas MacPherson,‡
Frederick Burkle, Jr.,§ Christophe Paquet,¶ Erich Kliewer,# and Patricia
Walker**
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †The
International Organization for Migration, Geneva, Switzerland; ‡St.
Joseph's Hospital, Hamilton, Ontario, Canada; §University of Hawaii,
Honolulu, Hawaii, USA; ¶Epicentre, Paris, France; #Manitoba Cancer
Treatment and Research Foundation, Winnipeg, Manitoba, Canada; and
**Regions Hospital, St. Paul, Minnesota, USA
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Each year, more than 15 million people seek political asylum or become
refugees in various parts of the world. Most of these displaced persons are
from developing countries where infectious diseases (e.g., tuberculosis,
hepatitis, malaria, various parasitic and emerging diseases) are prevalent.
These persons migrate mainly to the United States, Australia, and Canada,
nations that receive inflows of migrants proportional to their mainstream
population.
Because of the speed and efficiency of modern transportation systems,
health interventions applicable to all persons who cross international
borders are difficult to introduce and monitor. Identifying and addressing
individual and public health risks necessitate international and quarantine
health legislation, health policy and social economic evaluation,
risk-benefit and utility analysis, and risk-predictive modeling.
Ultimately, improving the health of migrants is at the heart of reducing
the public health risk to the international community from infectious
disease spread by travel.
Medical intelligence systems that can survey, detect, and confirm the
emergence of new infectious diseases are still in their infancy. The global
ability to generate numerators (cases of existing and emerging infectious
disease) has been limited to the relatively few diseases listed in the old
World Health Organization (WHO) International Health Regulations (yellow
fever, plague, cholera, smallpox); further limitations stem from poor
detection systems and incomplete reports (with the exception of smallpox).
The dynamic problem of defining numerators and denominators (displaced
persons at risk) is compounded by the need for improved diagnostics,
heightened recognition, and effective medical interventions for the
causative agents of diseases that affect these vulnerable populations.
Migrant populations have been displaced by disasters (natural, technologic,
and human), which test the public health resources of a nation and expose
weaknesses. Public health workers increasingly appreciate the fragile
interaction between individual host, environment, and infectious and
noninfectious agents capable of producing disease. The consequences of
these relationships, including the real and potential vulnerability of
populations, are becoming increasingly important indicators of national
security.
Cholera, a disease that affects migrant populations, was examined. In
Malawi, 11 outbreaks were documented in Mozambican refugees between 1987
and 1991, with attack rates of 0.6% to 9.3%. In 1994, an estimated 60,000
cases of cholera and 10,000 deaths occurred during a 1-month massive
epidemic among Rwandan refugees (population 800,000) in Goma, Democratic
Republic of Congo. Epidemic preparedness during the 1996 return of the
epidemic proved the cornerstone of cholera control in these refugees.
Properly implemented, active case-finding and rehydration therapy in
specialized treatment centers can keep the case-fatality ratio below 1%.
In Australia, use of hospital and medical services by immigrants and
refugees was examined. Foreign-born persons had lower hospitalization rates
than native Australians, although some immigrant groups had higher rates
for some diagnoses. Hospital data may help define trends in immigrant
disease profiles; the data, however, do not indicate whether the generally
lower hospitalization rates among immigrants were due to better health
status or to barriers in accessing the medical system. In the United
States, Minnesota has been a leader in refugee resettlement since 1979; one
center for international health has established a unique multidisciplinary
primary and specialty care program for refugees and immigrants. Hmong,
Cambodian, Vietnamese, Russian, Ukrainian, African, and Latin American
refugees and immigrants have been seen; diseases such as hepatitis B,
tuberculosis, and parasitic diseases, as well as mental health problems,
have been diagnosed; and prevention strategies or therapies have been
implemented.
Successful integration of migrant populations into their new communities'
health-care systems is critical to the prevention and control of new and
reemerging infectious diseases.
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Emerging Zoonoses
Frederick A. Murphy
University of California, Davis, California, USA
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In the past few years, emergent disease episodes have
increased; nearly all have involved zoonotic or species-jumping
infectious agents. Because there is no way to predict when or
where the next important new zoonotic pathogen will emerge or
what its ultimate importance might be, investigation at the
first sign of emergence of a new zoonotic disease is
particularly important. Such investigation may be described in
terms of a discovery-to-control continuum: from recognition of
a new disease in a new setting to complex phases involving the
hard science disciplines pertaining to discovery, the
epidemiologic sciences pertaining to risk assessment, and
activities pertaining to risk management. Today, many
activities involving zoonotic disease control are at risk
because of a failed investigative infrastructure or financial
base. Because zoonotic diseases are distinct, their prevention
and control will require unique strategies, based more on
fundamental research than on traditional approaches. Such
strategies require that we rebuild a cadre of career-committed
professionals with a holistic appreciation of several medical
and biologic sciences.
In the past few years, emergent disease episodes have increased in the
United States and globally. The list of important emergent diseases is
impressive indeed and, given what we know about disease ecology, it will
only continue to grow. Nearly all of these emergent disease episodes have
involved zoonotic infectious agents; that is, they have involved the
transmission of the etiologic agent to humans from an ongoing reservoir
life cycle in animals or arthropods, without the permanent establishment of
a new life cycle in humans. Fewer episodes have involved species-jumping by
the etiologic agent; that is, they derive from an ancient reservoir life
cycle in animals but have subsequently established a new life cycle in
humans that no longer involves an animal reservoir.
Distinct Prevention and Control Strategies
Nearly all of the major topics for discussion at this conference involve
either zoonotic or species-jumping infectious agents. Prevention and
control strategies for diseases caused by these agents are different from
those required for diseases whose etiologic agent has long relied on
human-to-human transmission for its survival. The Centers for Disease
Control and Prevention's (CDC) acute infectious disease prevention and
control strategies were largely developed from experiences with
vaccine-preventable childhood diseases, sexually transmitted diseases,
hepatitis, and other diseases for which traditional clinically based or
laboratory-based surveillance can provide the base for intervention
activities such as vaccination or antimicrobial chemotherapy. For the
zoonoses and for diseases caused by species-jumping agents, prevention and
control strategies have come from diverse bases. At the heart of this
research have been individual scientists who have spent whole careers
accumulating highly specialized knowledge and experience. In fact, the work
of these scientists might best be described as fundamental
research—research seeking the means for disease control and prevention.
Predicting the Emergence of Zoonotic and Species-Jumping Pathogens
In general, there is no way to predict when or where the next important new
zoonotic pathogen will emerge or what its ultimate importance might be. A
pathogen might emerge as the cause of a geographically limited curiosity,
intermittent disease outbreaks, or a new epidemic. No one could have
predicted the emergence or zoonotic nature of the bovine spongiform
encephalopathy prion in cattle in the United Kingdom in 1986, the emergence
or zoonotic potential of Sin Nombre virus as the cause of hantavirus
pulmonary syndrome in the Southwest in 1993, and certainly not the
species-jumping emergence of HIV as the cause of AIDS in 1981.
Consequently, investigation at the first sign of emergence of a new
zoonotic disease is particularly important, although the investigation
usually resembles a field- and laboratory-based research project rather
than a typical case-control-based outbreak investigation. This reality must
drive strategic planning for dealing with new zoonotic diseases.
Factors Contributing to the Emergence of Zoonotic Diseases
Many elements can contribute to the emergence of a new zoonotic disease:
microbial/virologic determinants, such as mutation, natural selection, and
evolutionary progression; individual host determinants, such as acquired
immunity and physiologic factors; host population determinants, such as
host behavioral characteristics and societal, transport, commercial, and
iatrogenic factors; and environmental determinants, such as ecologic and
climatologic influences.
Emergence of new zoonotic pathogens seems to be accelerating for several
reasons: global human and livestock animal populations have continued to
grow, bringing increasingly larger numbers of people and animals into close
contact; transportation has advanced, making it possible to circumnavigate
the globe in less than the incubation period of most infectious agents;
ecologic and environmental changes brought about by human activity are
massive; and bioterroristic activities, supported by rogue governments as
well as organized amateurs, are increasing, and in most instances the
infectious agents of choice seem to be zoonotic.
Ecologic Factors Contributing to the Emergence of Zoonotic Diseases, as
Exemplified by Arbovirus Diseases
Contributing to the emergence of zoonotic diseases is the capacity of
microorganisms and viruses to adapt to extremely diverse and changing
econiches. One of the most complex sets of adaptations concerns the
arboviruses and their transmission by specific arthropods. When ecosystems
are altered, disease problems of humans and animals follow. Population
movements and the intrusion of humans and domestic animals into arthropod
habitats have resulted in emergent disease episodes, some of which are the
stuff of fiction. The classic example is the emergence of yellow fever when
humans entered the Central American jungle to build the Panama Canal—many
contemporary examples suggest that similar events will continue to occur.
Deforestation and settlement of new tropical forest and farm margins have
exposed farmers and domestic animals to new arthropods and the viruses they
carry. Mayaro and Oropouche virus infections in Brazilian woodcutters who
cleared the Amazonian forest in recent years is a case in point. The
opening up of isolated ecosystems has contributed to emergent disease
episodes. Remote econiches, such as islands, with immunologically naive
potential reservoir hosts and vectors are often particularly vulnerable to
an introduced virus. For example, the initial Pacific island-hopping of
Ross River virus in the 1980s from its original econiche in Australia
caused "virgin soil" epidemics of arthritis-myalgia syndrome in Fiji and
Samoathis virus will surely reemerge. Increased long-distance air travel
facilitates the movement of infected persons and exotic arthropod vectors
around the world. The introduction of the Asian mosquito Aedes albopictus
to the United States in water contained in used tires represents an
unsolved problem of this kind. Increased long-distance livestock
transportation facilitates the movement of viruses and arthropods
(especially ticks) around the world. The introduction and emergence of
African swine fever virus from Africa into the Americas in the 1960s and
1970s seem prophetic; although this virus is not zoonotic (it does not
infect humans), this experience should raise the question concerning
possible transport of Crimean-Congo hemorrhagic fever virus or other
tick-borne pathogens to new locales. Ecologic factors pertaining to
uncontrolled urbanization and environmental pollution are contributing to
many emergent disease episodes. Arthropod vectors breeding in accumulations
of water (e.g., tin cans, old tires) and sewage-laden water are a problem
worldwide. Environmental chemical toxicants (herbicides, pesticides,
residues) can also affect vector-virus relationships directly or
indirectly. Ecologic factors related to expanding primitive irrigation
systems are becoming important in virus disease emergence, as exemplified
by the emergence of Japanese encephalitis in newly developed rice-growing
areas of southern Asia. New routings of long-distance bird migrations,
brought about by new man-made water impoundments, represent an important
yet still untested risk of introduction of arboviruses into new areas.
Global warming, which affects sea level, estuarine wetlands, fresh water
swamps, and human habitation patterns, may also be affecting vector-virus
relationships throughout the tropics; however, data are scarce and
long-term programs to study the effect of global warming have too often not
included the participation of tropical medicine experts.
Of all the ecologic factors contributing to arthropod-borne zoonotic viral
disease emergence, uncontrolled urbanization is the most important. The
mega cities of the tropics, with their lack of sanitary systems, serve as
incubators for emerging zoonoses—they represent the most difficult zoonotic
disease risks of the next century. Who will pay to control disease in these
cities? How will the World Health Organization (WHO) and the Pan American
Health Organization (PAHO) serve the needs of the people in these cities?
How will CDC serve the interests of the people of the United States in
preventing emergent zoonotic diseases from emigrating from these cities?
Lessons from the past suggest that we need a larger national and
international enterprise to deal with emergent zoonoses in such settings,
but even more we need an adaptable enterprise, one that can adjust quickly
to diverse episodes.
Lessons from Venezuelan Equine Encephalitis Epidemics
Past Venezuelan equine encephalitis epidemics provide lessons regarding
today's zoonotic disease prevention and control systems. In 1971, as the
virus crossed from Mexico into Texas, agricultural disease control
authorities were prepared to start shooting and burying horses in a massive
slaughter campaign. Scientists from CDC and the Middle America Research
Unit (at the time a unit of the National Institutes of Health) provided the
virologic and epidemiologic base to override the sanitary rifle strategy of
agricultural authorities, and the U.S. Army provided its then new TC83
vaccine. Conflict between agricultural and public health agencies was
rampant; if this kind of emergency happened again, the response might not
be much different. If the epidemic in Venezuela and Colombia in 1995 had
progressed and jumped north, which agency would have stepped forward to
direct control activities? What would have been done? Do we have an
interagency plan? The same question might be asked in regard to the
possible introduction of Rift Valley fever virus into the United States. In
my view, our government institutional culture fails in long-term,
interdisciplinary, interagency strategy development—we need strategies that
are proof-tested to ensure success.
There is another lesson from the 1971 and 1995 Venezuelan equine
encephalitis epidemics. Thirty years ago the arbovirus community was large,
very experienced in field work and disease control actions, and holistic in
perspective and expertise. Arbovirologists were able to bring together all
necessary expertise—entomology and vector biology, ecology, mammology,
ornithology, epidemiology, and virology. However, today this community,
like so many others supporting zoonotic public health programs, is very
small, rather poorly experienced in field work, and scientifically
fragmented. Experts on mosquito biology, genetics, ecology, and vector
competence are becoming more and more separated from the people in local
mosquito control agencies who are expected to terminate epidemics. We had
better fix this, organizationally and culturally, if we are to deal with
mosquito-borne diseases in the 21st century.
Lessons from the Equine Morbillivirus Outbreak in Australia
Recent experiences in Australia with a new morbillivirus disease add still
more lessons in zoonotic disease prevention and control. In 1994, horses on
a property in Queensland developed acute respiratory distress with
hemorrhagic manifestations—14 of 21 infected horses died. A horse trainer
and a stable-hand became ill after nursing a sick horse—the trainer died.
The disease was found to be caused by a previously unknown morbillivirus.
Remarkably, in 1996 fruit bats (flying foxes) were found to be the natural
host of the virus. Studies are under way to unravel these findings.
One lesson is similar to that taught by experiences with Venezuelan equine
encephalitis. In Australia, where animal disease research is organized on a
national basis but human disease research (and prevention and control
activities) on a state basis, this disease was given over to the Australian
Animal Health Laboratory. One can imagine the public outcry if it had
turned out that humans were at greater risk than horses. Again, cooperation
across a wide range of institutions is required to deal with zoonoses, but
when human health is at risk, I cannot imagine our public health
institutions deferring to animal disease and agricultural institutions.
Similar turf issues have been raised in the United States and in the United
Kingdom in regard to the recent episode of H5N1 influenza in chickens and
humans in Hong Kong.
Lessons from Ebola Hemorrhagic Fever Epidemics
Should we be concerned about Ebola virus? Is there a risk to Africa that
compares with the everyday problems of other zoonoses such as malaria or
yellow fever? Is there a risk to people in North America or Europe? If the
worst that might happen is an occasional importation resulting in a small
cluster of cases, should we be concerned? If the time and place of such
episodes are unpredictable, should we not just wait and react after the
fact? The risk reflected in these questions is difficult to evaluate
because we know so little. However, we can say that as western-style
hospitals become more affordable for Africans, nosocomial Ebola
amplification will increase, and epidemics will get larger.
These viruses and the diseases they cause need to be understood because the
risk they represent is unknown and the risk for future episodes is so
unpredictable—the same should be said in regard to all similarly lethal
zoonotic pathogens. For example, we need to find the natural reservoir of
Ebola virus and learn how its prevalence in its natural environment and how
transmission to humans are regulated. In Africa, the emergence of Ebola
virus could dramatically increase if its still unknown reservoir host(s)
increased, the virus changed its behavior, or ecologic factors brought
additional reservoir hosts into play. We need to know enough to detect such
changes quickly. The concerned public would not be satisfied if public
health leaders decided on a wait-and-see approach for dealing with Ebola
hemorrhagic fever or other diseases with similar pathogenic potential.
Dealing with Ebola virus and similar very dangerous infectious agents need
not be thought of as so expansive or expensive as to be unrealistic.
Field-based epidemiologic studies are needed; diagnostic systems require
better placement in laboratories in Africa. Training is a major need—not
through short courses, but rather through advanced career training and
experience; transcending these is the need for an expanded research base,
which in turn requires more national laboratory facilities and resources
for work at biosafety level (BSL) 4. These needs must be met in all
industrialized countries on behalf of developing countries.
Lessons from Rabies Epidemics
Rabies provides many lessons in how viral adaptation contributes to
emergence in new econiches. Often, the necessary ecologic elements are in
place and the recipe for emergence simply involves the introduction of
virus; a dramatic illustration was the appearance of epidemic raccoon
rabies in the eastern United States. The epidemic was traced to raccoons
imported from Florida to West Virginia in 1977—as usual, human perturbation
of an ecosystem, in this instance involving the transport of wild raccoons
from an endemic site, caused trouble. One key to our understanding of this
episode was the discovery that rabies virus is not one virus; rather, it is
a set of different genotypes, each transmitted within a separate reservoir
host econiche. In North America, there are six terrestrial animal
genotypes, including the raccoon virus genotype. Raccoons bite raccoons
that bite raccoons, and after some time, their virus becomes a distinct
genotype, highly adapted to the host cycle. When the full significance of
this discovery was realized, many mysteries of rabies ecology were
clarified. The lesson here is that modern virologic research is the key for
prevention and control programs such as those carried out by the CDC Rabies
Laboratory and the Texas State Health Department, which is achieving much
success with its coyote vaccination program.
Lessons from the Hantavirus Pulmonary Syndrome Epidemic
In 1993, hantavirus pulmonary syndrome was first recognized in the
southwestern United States. Cases have been found in 28 states; as of 1997,
more than 164 cases had been confirmed in the United States and more than
400 throughout the Americas—the death rate has been approximately 45%. At
the beginning of the investigation, serologic tests provided the first clue
about the nature of the causative virus. Viral RNA was amplified from
patient specimens, and a previously unknown hantavirus, now named Sin
Nombre virus, was uncovered. Later, scientists from CDC, the University of
New Mexico, and elsewhere found that several variant viruses were
distributed over large areas of the United States, all previously unknown,
all entrenched in specific rodent reservoirs, all capable of zoonotic
transmission to humans.
The laboratory and field work resembled fundamental field- and
laboratory-based research, not a traditional outbreak investigation. Sin
Nombre virus and its relatives could only be dealt with in laboratories
with the most sophisticated molecular biologic and immunologic
technologies, the most expert staff scientists, and the kind of global
perspective seen in WHO international reference centers. If scientists in
these laboratories compete rather than collaborate, how will public health
be given priority? How will technology transfer occur as rapidly as needed?
How will the full capacity of more specialized biomedical research
laboratories be brought to bear?
The tradition of public service holds the answer. When the rabies
immunofluorescence test was developed at CDC, it was made available
immediately to state and other laboratories. When Legionella pneumophila
was discovered, cultures and reagents were made available immediately to
everyone concerned. This tradition, in turn, has led over the years to the
immediate transfer to CDC of new infectious agents isolated in other
laboratories—Marburg virus from Germany, Lassa virus from Yale, HIV from
France, poliovirus isolates from everywhere. Research competition has never
been the point—public health has been the purpose at hand. The perpetuation
of this tradition seems extremely important.
Lessons from the Bovine Spongiform Encephalopathy Epidemic in Cattle and
New-Variant Creutzfeldt-Jakob Disease in Humans
Bovine spongiform encephalopathy (BSE) in the United Kingdom may provide
more lessons than any other recent emergent zoonotic disease episode. The
disease was first diagnosed in the United Kingdom in 1986; as of 1997, more
than 170,000 cattle had been reported as infected, but modern statistical
methods have indicated that about one million cattle had been infected,
roughly half of which entered the human food chain in the United Kingdom.
Today, with the wisdom of hindsight, it might be said that the ministry of
agriculture in the United Kingdom failed to react in time to what was
clearly a great risk to the livestock and related food industries of the
country—every element of its disease prevention and control
responsibilities might be called into question. By 1990, the front pages of
British newspapers were filled with BSE articles, forcing the question
"…does BSE pose a risk to human health?" British government officials
responded, "…there is nothing to worry about…" This of course led the
public to become more skeptical. The editors of the journal Nature reacted
as follows:
…Never say there is no danger [risk]. Instead, say that there is always
a danger [risk], and that the problem is to calculate what it is… Never
say that the risk is negligible unless you are sure that your listeners
share your own philosophy of life…
In my view, this response sums up one of the central precepts of public
health practice.
In 1995, the BSE agent was reported to be the cause of a new human zoonotic
disease, new-variant Creutzfeldt-Jakob disease. By 1997, 26 cases had been
reported in the United Kingdom and one in France. A recent report from The
Royal Society states that there is now a compelling case regarding
new-variant Creutzfeldt-Jakob disease as the human manifestation of BSE.
With such a small number of cases, it is impossible to predict future
numbers of cases of the human disease, but clearly the damage to the
livestock and related food industries of the United Kingdom will continue.
BSE may be instructive in other ways, especially in its extension into the
worlds of macroeconomics, international trade, political science, and even
global governance.
In all these lessons, one of the most important points is the need for
greater epidemiologic resources and better trained professionals for
dealing with human and animal diseases or with the zoonotic interface
between the two. This training component requires consideration of all
steps along the discovery-to-control continuum.
The Discovery-to-Control Continuum as Applied to Zoonotic Diseases
Initial investigation at the first sign of emergence of a new zoonotic
disease must focus on practical characteristics such as death rate,
severity of disease, transmissibility, and remote spread, all of which are
important predictors of epidemic potential and societal risk. Various
elements of a discovery-to-control continuum are usually called for:
discovery, the recognition of a new zoonotic disease in a new setting;
epidemiologic field investigation; etiologic investigation; diagnostics
development; focused research; technology transfer; training and outreach;
and ultimately control, elimination, and eradication. Of course, not all of
these elements are appropriate in every emerging zoonotic disease
episode—decisions must be made and priorities must be set.
In the initial phases in the discovery-to-control continuum, people outside
the "citadel" (the traditional federal community of investigators and
officials) must be recognized—local clinicians, pathologists (including
medical examiners and forensic pathologists), veterinarians and animal
scientists, ecologists, wildlife scientists, as well as local public health
officials, many of whom have not been enamored of their experiences in
dealing with those inside the citadel. The important early role of primary
diagnostic laboratories and the reference laboratory networks that support
them must also be recognized. In this era of the primacy of molecular
microbiology and virology, it bears reminding that many of the early
investigative activities surrounding the identification of a possibly
emergent zoonotic disease must be carried out in the field, not in the
laboratory. This is the world of shoe-leather epidemiology (the logo of
CDC's Epidemic Intelligence Service program is the outline of the sole of a
shoe with a prominent hole worn in it), as well as of molecular
microbiology and virology.
In the intermediate phases in the discovery-to-control continuum, the
continuum progresses to the general area of risk management, the area
represented not by the question what's going on here? but by the question
what are we going to do about it? This phase may include expansion of many
elements: technology transfer involving diagnostics development and proof
testing, vaccine and drug development and proof testing, sanitation and
vector control, and medical and veterinary care activities and their
adaptation to the circumstances of the disease locale; commercialization,
where appropriate, of diagnostics, vaccines, and therapeutic agents in
quantities needed and provision of these materials through nongovernment
organizations or government sources; training, outreach, continuing
education, and public education, each requiring professional expertise and
adaptation to the special circumstances of the disease locale; and
communications, employing the technologies of the day such as the Internet
and professional expertise.
Further along the discovery-to-control continuum, activities become more
complex. Frustration often occurs at intermediate points as administrators
and politicians drag their feet in regard to resource allocation. This
frustration, in turn, drives scientists back to their laboratories, to the
world of research, to the front end of the continuum. Younger scientists,
particularly, become cynical of the harsh political world of risk
management, even though this is the arena in which their discoveries must
prove themselves.
More expensive and specialized expertise and resources come into play in
the final phases of the discovery-to-control continuum: public health
systems, including rapid case-reporting systems, surveillance systems,
vital records and disease registers, staffing and staff support, logistic
support, legislation and regulation, and expanded administration; special
clinical systems, including isolation of cases, quarantine, and patient
care; and public infrastructure systems, including sanitation and sewerage,
safe food and water supplies, and reservoir host and vector control.
The question of facilities needs in the United States is an element of our
capacity to fulfill the discovery-to-control continuum. What about BSL-3+
and BSL-4 laboratory facilities west of the Appalachians? Recent debate
makes it clear that having two BSL-4 facilities in the United States (CDC
in Atlanta, and the U.S. Army Medical Research Institute of Infectious
Diseases in Frederick, Maryland) and one in Canada (at the new center in
Winnipeg) is not enough. Plans for a few small BSL-4 labs in U.S. academic
centers may help in expanding basic research supported by competitive
grants, but they will not support expanded field-based research. Which
government agency will step forward to solve this problem? And in a related
way, which government agency will step forward to solve the unique problem
of career-committed professional personnel needs for dealing with emerging
zoonotic diseases?
Conclusions
Who will be the world's doctor? Who will be the world's expert on zoonotic
diseases? These questions are taken from an editorial in the New York
Times, May 12, 1995. It seems that many authorities, including those at
CDC, are saying that they have the answer to these questions in regard to
all emerging diseases. Their answers have been in the form of proposals and
funding requests to expand global disease surveillance, diagnostics,
communications, and emergency response systems, a global training program,
and a global stable funding base. However, somewhat distinct strategies are
needed to deal specifically with emerging zoonotic diseases, and these
strategies have not been fully developed. Examples have been given in this
paper to suggest that these strategies must involve more of a field and
laboratory research enterprise than a traditional surveillance and
reference diagnostics enterprise. In some cases, it is not even clear who
might do the focused applied research that must underpin advances in
zoonotic disease prevention and control. In present circumstances, where
the survival of institutions is at stake, turf battles are exacerbated, and
competition rather than cooperation between academic institutions and
government agencies ensues. CDC may be getting new funds, but there is no
parallel sense of "good times ahead" out in the country. This is happening
in contradiction to public expectations. Data clearly show that the
concerned public wants more disease control and intervention actions, more
of the medical research needed to drive such actions, and more
participation across the country. Numerous surveys of public opinion done
by Research!America show that the concerned public is willing to pay. In my
view, public expectations can only be met by the integration of the nascent
global public health emerging infectious disease network, with networks
focused on threats posed by livestock animal diseases, crop plant diseases,
and bioterrorism. The public would see such an overall system as having a
high benefit:cost ratio, which would solve several high priority problems
most efficiently.
Frederick Murphy is professor of virology at the School of Veterinary
Medicine, University of California, Davis. He has served as director of the
Division of Viral and Rickettsial Diseases as well as director of the
National Center for Infectious Diseases, Centers for Disease Control, and
dean of the School of Veterinary Medicine, UC Davis. His professional
interests include the pathogenesis and ultrastructural pathology of viral
diseases, viral characterization and taxonomy, rabies, arboviruses, viral
hemorrhagic fevers, viral encephalitides, public health policy, vaccine
development, and new and reemerging infectious diseases.
Address for correspondence: Frederick A. Murphy, School of Veterinary
Medicine, University of California, Davis, CA 95616-8734, USA; fax:
530-752-2801; e-mail: famurphy@ucdavis.edu.
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Influenza: An Emerging Disease
Robert G. Webster
St. Jude Children's Research Hospital, Memphis, Tennessee, USA
---------------------------------------------------------------------------
Because all known influenza A subtypes exist in the aquatic
bird reservoir, influenza is not an eradicable disease;
prevention and control are the only realistic goals. If people,
pigs, and aquatic birds are the principal variables associated
with interspecies transfer of influenza virus and the emergence
of new human pandemic strains, influenza surveillance in these
species is indicated. Live-bird markets housing a wide variety
of avian species together (chickens, ducks, geese, pigeon,
turkeys, pheasants, guinea fowl), occasionally with pigs, for
sale directly to the public provide outstanding conditions for
genetic mixing and spreading of influenza viruses; therefore,
these birds should be monitored for influenza viruses.
Moreover, if pigs are the mixing vessel for influenza viruses,
surveillance in this population may also provide an early
warning system for humans.
The influenza virus continues to evolve, and new antigenic variants (drift
strains) emerge constantly, giving rise to yearly epidemics. In addition,
strains to which most humans have no immunity appear suddenly, and the
resulting pandemics vary from serious to catastrophic.
Influenza viruses are unique among respiratory tract viruses in that they
undergo considerable antigenic variation. Both surface antigens of the
influenza A viruses undergo two types of variation: drift and shift (1).
Antigenic drift involves minor changes in the hemagglutinin (HA) and
neuraminidase (NA), whereas antigenic shift involves major changes in these
molecules resulting from replacement of the gene segment.
The Reservoirs of Influenza A Viruses
Aquatic birds are the reservoirs of all 15 subtypes of influenza A viruses.
In wild ducks, influenza viruses replicate preferentially in the cells
lining the intestinal tract, cause no disease signs, and are excreted in
high concentrations in the feces (up to 10(sup 8.7) 50% egg infectious doses/g)
(2). Avian influenza viruses have been isolated from freshly deposited
fecal material and from unconcentrated lake water, which indicates that
waterfowl have a very efficient way to transmit viruses, i.e., by fecal
material in the water supply. Since a large number of susceptible young
ducks are hatched each year throughout the world, many birds are infected
by virus shed into water. This would explain the high incidence of virus
infection in Canadian ducks, particularly juveniles, when up to 30% can
shed virus before fall migration. Transmission by feces also provides a way
for wild ducks as they migrate through an area to spread their viruses to
other domestic and feral birds (3).
The avirulent nature of avian influenza infection in ducks and wading birds
may result from virus adaptation to this host over many centuries, which
created a reservoir that ensures perpetuation of the virus; therefore,
ducks and wading birds may be occupying an important position in the
natural history of influenza viruses. Influenza viruses of avian origin
have been implicated in outbreaks of influenza in mammals, such as seals
(4), whales (5), and pigs (6), as well as in domestic poultry (7).
Evolutionary Pathways for Influenza Viruses
Studies on the ecology of influenza viruses have led to the hypothesis that
all mammalian influenza viruses derive from the avian influenza reservoir.
Support for this theory comes from phylogenetic analyses of nucleic acid
sequences of influenza A viruses from a variety of hosts, geographic
regions, and virus subtypes. Analyses of the nucleoprotein (NP) gene show
that avian influenza viruses have evolved into five host-specific lineages:
ancient equine, which has not been isolated in over 15 years; recent
equine; gull; swine; and human. The human and classic swine viruses have a
genetic "sister group" relationship, which shows that they evolved from a
common origin. The ancestor of the human and classic swine virus appears to
have been an intact avian virus that, like the influenza virus currently
circulating in pigs in Europe, derived all its genes from avian sources
(8,9).
Studies on the NP and other gene lineages in avian species show separate
sublineages of influenza in Eurasia and the Americas, indicating that
migratory birds moving between these continents (latitudinal migration)
have little or no role in the transmission of influenza, while birds that
migrate longitudinally appear to play a key role in the continuing process
of virus evolution.
Phylogenetic analyses of amino acid changes show that avian influenza
viruses, unlike mammalian strains, have low evolutionary rates (8). In
fact, influenza viruses in aquatic birds appear to be in evolutionary
stasis, with no evidence of net evolution over the past 60 years.
Nucleotide changes have continued at a similar rate in avian and mammalian
influenza viruses; however, these changes no longer result in amino acid
changes in the avian viruses, whereas all eight mammalian influenza gene
segments continue to accumulate changes in amino acids. The high level of
genetic conservation suggests that avian viruses are approaching or have
reached optimum, wherein nucleotide changes provide no selective advantage.
It also means that the source of genes for pandemic influenza viruses
exists phenotypically unchanged in the aquatic bird reservoir. The most
important implication of phylogenetic studies is that the ancestral viruses
that caused the Spanish flu in 1918, as well as the viruses that provided
gene segments for the Asian/1957 and Hong Kong/1968 pandemics, are still
circulating in wild birds, with few or no mutational changes.
Emergence and Reemergence of "New" Influenza A Virus in Humans
Over the past two and a half centuries, 10 to 20 human influenza pandemics
have swept the globe; the most devastating, the so-called Spanish flu of
1918 to 1919, caused more than 20 million deaths and affected more than 200
million people. Both pandemics probably originated from aquatic birds.
Since the first human influenza virus was isolated in 1933, new subtypes of
human type A influenza viruses have occurred: H2N2 (Asian influenza)
replaced H1N1 in 1957, Hong Kong (H3N2) virus appeared in 1968, and H1N1
virus reappeared in 1977. Each of these new subtypes first appeared in
China, and anecdotal records suggest that previous epidemics also had their
origin in China. Serologic and virologic evidence suggests that since 1889
there have been six instances of the introduction of a virus bearing an HA
subtype that had been absent from the human population for some time. Three
human subtypes of HA have appeared cyclically—H2 viruses in 1889, H3 in
1900, H1 in 1918, H2 again in 1957, H3 again in 1968, and H1 again in 1977.
Phylogenetic evidence indicates that a totally new H1N1 virus of avian
origin (not a reassortant) could have appeared in humans or swine before
the 1918 influenza and replaced the previous human virus strains. Whether
the virus was first introduced into humans and then transmitted to pigs, or
vice versa, remains unknown. The reappearance of the H1N1 Russian 1977
influenza virus remains a mystery.
How Are Influenza Viruses Spread?
Avian influenza viruses in wild aquatic birds are spread by fecal-oral
transmission through the water supply (10); initial transmission of avian
influenza viruses to mammals, including pigs and horses, probably also
occurs by fecal contamination of water. Scholtissek has postulated that the
use of fecal material from ducks for fish farming in Asia may contribute to
transmission of avian influenza viruses to pigs (11). Another direct method
of transfer is by feeding pigs untreated garbage or the carcasses of dead
birds. Raising pigs under chicken houses and feeding them dead avian
carcasses has been observed on rare occasions in the United States; H5N2
influenza virus was isolated from pigs living under chicken houses in
Pennsylvania during the outbreak in 1982. Both pigs and poultry are
commonly raised on the same commercial farms. From the perspective of the
control of interspecies transmission of influenza, this is undesirable, for
it may facilitate interspecies transmission of influenza viruses. After
transmission to pigs, horses, or humans, the method of spread of influenza
is mainly respiratory.
Emergence of H5N2 Influenza Viruses in North America
In 1983 an H5N2 influenza virus infected chickens and turkeys in
Pennsylvania and became highly pathogenic for poultry. Virologic and
serologic studies provided no evidence of transmission to humans (12). The
virus was eventually eradicated by quarantine and extermination of more
than 17 million birds at a direct cost of more than US$60 million and an
indirect cost to the industry of more than US$250 million.
More recently, a highly pathogenic H5N2 influenza virus emerged in domestic
chickens in Mexico (7). In October 1993, egg production decreased and
deaths increased among Mexican chickens in association with serologic
evidence of an H5N2 influenza virus. H5N2 virus was isolated in May 1994.
By the end of 1994, the virus had mutated to contain a highly cleavable HA,
but remained only mildly pathogenic in chickens. Within months, however, it
had become lethal in poultry. Phylogenetic analysis of the HA of H5 avian
influenza viruses, including the Mexican isolates, indicated that the
epidemic virus had originated from the introduction of a single virus of
the North American lineage into Mexican chickens (Figure 1). This virus was
eradicated from chickens by quarantine and use of inactivated vaccine.
[Fig]
Figure 1. Molecular changes associated with emergence of a
highly pathogenic H5N2 influenza virus in chickens in Mexico. In 1994,
a nonpathogenic H5N2 influenza virus in Mexican chickens was related to
an H5N2 virus isolated from shorebirds (ruddy turnstones) in Delaware Bay,
United States, in 1991. The 1994 H5N2 isolates from chickens replicated
mainly in the respiratory tract, spread rapidly among chickens, and
were not highly pathogenic. Over the next year the virus became highly
pathogenic, and the hemagglutinin acquired an insert of two basic amino
acids (Arg-Lys), possibly by classic recombination and a mutation of Glu
to Lys at position – 3 from the cleavage site of HA1/HA2.
Live Bird Markets and the Epidemiology of Influenza
The chicken/Pennsylvania (H5N2) influenza outbreak in 1983 to 1984
demonstrated that live bird markets play an important part in the spread of
influenza viruses in avian species. In 1992, Senne et al. (13) described live bird
markets as the "missing link in the epidemiology of avian influenza," for H5N2
viruses had been isolated from live birds until 1986. These H5N2 viruses caused
subclinical infection in chickens in the markets, as did H5N1 viruses in live bird
markets in Hong Kong in 1997 (Figure 2). Moreover, ducks in the markets in the
United States were infected with many different subtypes of influenza A viruses,
including H2N2 viruses related antigenically to the Asian/57 (H2N2) viruses that
have disappeared from humans.
[Fig]
Figure 2. The emergence of H5N1 influenza in Hong Kong. It is postulated that
a nonpathogenic H5N1 influenza spread from migrating shorebirds to ducks by
fecal contamination of water. The virus was transmitted to chickens and became
established in live bird markets in Hong Kong. During transmission between
different species, the virus became highly pathogenic for chickens and
occasionally was transmitted to humans from chickens in the markets. Despite
high pathogenicity for chickens (and humans), H5N1 were nonpathogenic for
ducks and geese.
The live bird markets in the United States continue to harbor many influenza
viruses. The ancestor of the H5N2 influenza virus that caused the epidemic in
Mexico in 1993 to 1995 was isolated from market birds, and H7NX subtypes are
still found in live bird markets. These viruses are potentially pathogenic for
chickens and are of great concern to chicken farmers in the northeastern United
States. The depopulation of live bird markets and farms in the New Territories of
Hong Kong (December 29, 1997) stopped the spread of H5N1 influenza viruses.
An important lesson can be learned from this action in Hong Kong. Live bird
markets are potential breeding grounds for both avian and mammalian influenza
viruses. Serologic monitoring of the chickens in Hong Kong markets for H5N1
influenza virus was an important first step in stopping the spread of the viruses.
An even more important step would be to reduce the opportunity for interspecies
transmission by marketing chickens separately from other avian species.
The Index Case of H5N1 in Humans in Hong Kong
On May 21, 1997, a 3-year-old boy from Hong Kong died in an intensive care
unit in Hong Kong on the fifth day of his hospitalization, with a final
diagnosis of Reye syndrome, acute influenza pneumonia, and respiratory
distress syndrome (14). He had no indications of other underlying disease,
including immunodeficiency or cardiopulmonary disease. From a tracheal
aspirate, we isolated an influenza virus in MDCK cells but were unable to
grow any pathogenic bacteria from respiratory specimens. In
hemagglutination inhibition assays, the virus did not react with ferret
antisera to recent isolates of human and swine subtypes.
Hemagglutination inhibition assays using antisera to 14 H subtypes showed
that the isolate was an H5 influenza A virus. Neuraminidase inhibition
tests, using antisera to nine N subtypes, indicated that the neuraminidase
was of the N1 subtype. Nucleotide sequence analyses of parts of the HA and
NA genes of the virus allowed a phylogenetic comparison with other
influenza viruses. Our analyses confirmed that the virus was of the H5N1
subtypes. Each of the eight RNA segments was of avian origin, and the virus
was highly pathogenic for chickens. The contribution of the influenza A
H5N1 virus infection to the child's disease, eventually leading to death,
was complicated by the child's treatment with aspirin. The virus
identification is important because it is the first documented isolation of
an influenza A virus of this subtype from humans (15).
Characterization of the Human and Chicken H5N1 Viruses from Hong Kong
Avian influenza outbreaks occurred in Hong Kong from late March to early
May of 1997. Three chicken farms were separately affected; the death rate
for the total of 6,800 chickens exceeded 70%. A comparison between the
nucleotide sequences of the H5 genes from both the human virus A/Hong
Kong/156/97 (H5N1) (HK97) and a representative of the chicken viruses from
the March outbreak, A/chicken/Hong Kong/258/97 (CkHK97), showed a high
degree of homology in their respective H5 HA1 sequences. Only three
amino-acid differences were observed in the HA1 of the HA, confirming the
close phylogenetic relationship between these viruses, belonging to the
Eurasian lineage of the subtype H5 viruses.
Sequence analyses of the HA of multiple human and chicken H5N1 isolates
show that they form two subgroups with close linkage between chicken and
human isolates. An analysis of the amino acids expected to be involved in
the assembly of the receptor binding site showed no differences could be
observed between the human isolate and avian H5 viruses. Therefore, the H5
HA of HK97 had probably not acquired mutations that favor binding to sialic
acids with 2,6 linkage to the galactoside over the 2,3 linked sialic acid
receptor preferred by human and avian viruses respectively. However, the
loss of a potential N-linked glycosylation site at amino acid 156 Asn,
close to the receptor binding site, could affect binding to the cellular
receptor.
The amino acid sequence motif at the cleavage site of the HA molecule has
been associated with high virulence of avian influenza viruses.
Experimental infection of chickens with HK97 showed that even after
passaging in mammalian cells (once in the child and twice in MDCK cells),
the virus remained highly pathogenic for chickens: all eight chickens
inoculated intratracheally with MDCK-grown HK97 died within 3 days after
infection. A comparison of the reactivity of a panel of 17 monoclonal
antibodies (MAb) directed against A/chicken/Pennsylvania/83 (H5N2) with
HK97 and CkHK97 in a hemagglutination inhibition assay showed similar
antigenic reactivities with all but one MAb, indicating antigenic
cross-reactivity between these viruses and the usefulness of these
antibodies for diagnosis.
The fetuin-cleaving activity of the NA proved to be inhibited by anti-NA
antiserum. Reverse transcriptase polymerase chain reaction using primer
sets that amplified the 5' end of the NA gene segments showed that this
gene was of the N1 genotype. Nucleotide sequence analysis and comparison to
published NA sequences confirmed this finding genetically. The NA sequences
unequivocally showed a close molecular relationship between HK97 and
CkHK97, as a unique 57-nucleotide deletion was observed in the stalk region
of the N1 gene of both viruses. Each of the eight gene segments showed
close genetic homology between the HK97 and Ck/HK97 viruses, the lowest
being 98.2% for the nucleoprotein; the remaining genes varied from 98.8% to
100% homology (16).
Can the Emergence of Pandemic Strains Be Prevented?
Because all known influenza A virus subtypes are found in aquatic wild
birds in nature, agricultural authorities have recommended avoiding direct
or indirect contact between domestic poultry and wild birds. A classic
mistake made by chicken and turkey farmers is to raise a few domestic ducks
on a pond near poultry barns; these birds attract wild ducks. The highly
pathogenic outbreaks of H5N2 avian influenza in chickens and turkeys in
Pennsylvania and surrounding states in 1983 to 1984 (12) and the H5N2 in
Mexico in 1993 (7) could probably have been prevented if domestic poultry
had been raised in ecologically controlled houses with a high standard of
security and limited access.
If we assume that people, pigs, and aquatic birds are the principal
variables associated with the emergence of new human pandemic stains, human
pandemics of influenza may be prevented. The principles applied to
preventing outbreaks of influenza in domestic animals should apply equally
here. Pandemic strains of human influenza emerge only rarely; however,
interspecies transmission of influenza viruses may not be so rare, for up
to 10% of persons with occupational exposure to pigs develop antibodies to
swine influenza virus (17). Most transfers of influenza viruses from pigs
to humans are dead-end transfers (they do not spread efficiently from human
to human). As indicated above, we do not know the frequency of virus
transfer between the suspect species in southern China. If there is an
epicenter for pandemic influenza and a detectable frequency of transfer
between people, pigs, and ducks and if we understand the ecologic and
agricultural features involved in the transfer, pandemics may be
preventable. If pigs are the major mixing vessel for influenza viruses,
changes in the agricultural practices that separate pigs from people and
ducks could prevent future pandemics. Most importantly, we may influence
the appearance of pandemics by changing the methods of live bird marketing
by separating chickens from other species, especially from aquatic birds.
This work was supported by Public Health Service grants AI-29680 and
AI-08831 from the National Institute of Allergy and Infectious Diseases, by
Cancer Center Support (CORE) grant CA-21765, and by the American Lebanese
Syrian Associated Charities.
Dr. Webster holds the Rose Marie Thomas Chair in the Department of
Virology and Molecular Biology at St. Jude Children's Research Hospital,
Memphis, Tennessee. In addition, he is director of the World Health
Organization Collaborating Center for Ecology of Influenza Viruses in Lower
Animals and Birds. He has devoted his life to the understanding of the
emergence of pandemic influenza viruses, the structure and function of the
viral proteins, and methods for developing new and improved antiviral drugs
and vaccines.
Address for correspondence: Robert G. Webster, St. Jude Children's Research
Hospital, 332 North Lauderdale St., Memphis TN 38105-2794, USA; fax:
901-523-2622; e-mail: robert.webster@stjude.org.
References
1. Murphy BR, Webster RG. Orthomyxoviruses. In: Fields BN, Knipe DM,
Howley PM, Chanock RM, Melnick JL, Monath TP, Roizman R, Straus SE,
editors. Fields virology. New York: Raven Press; 1996. p. 1397-445.
2. Webster RG, Yakhno MA, Hinshaw VS, Bean WJ, Murti KG. Intestinal
influenza: replication and characterization of influenza viruses in
ducks. Virology 1978;84:268-78.
3. Halvorson D, Karunakaran D, Senne D, Kelleher C, Bailey C, Abraham A,
et al. Epizootiology of avian influenza-simultaneous monitoring of
sentinel ducks and turkeys in Minnesota. Avian Dis 1983;27:77-85.
4. Geraci JR, St. Aubin DJ, Barker IK, Webster RG, Hinshaw VS, Bean WJ,
et al. Science 1982;215:1129-31.
5. Hinshaw VS, Bean WJ, Geraci JR, Fiorelli P, Early G, Webster RG.
Characterization of two influenza A viruses from a pilot whale. J
Virol 1986;58:655-6.
6. Scholtissek C, Burger H, Bachmann PA, Hannoun C. Genetic relatedness
of hemagglutinins of the H1 subtype of influenza A viruses isolated
from swine and birds. Virology 1983;129:521-3.
7. Horimoto T, Rivera E, Pearson J, Senne D, Krauss S, Kawaoka Y, et al.
Origin and molecular changes associated with emergence of a highly
pathogenic H5N2 influenza virus in Mexico. Virology 1995;213:223-30.
8. Gorman OT, Bean WJ, Kawaoka Y, Webster RG. Evolution of the
nucleoprotein gene of influenza A virus. J Virol 1990;64:1487-97.
9. Gammelin M, Altmuller A, Reinhardt U, Mandler J, Harley VR, Hudson PJ,
et al. Phylogenetic analysis of nucleoproteins suggests that human
influenza A viruses emerged from a 19th-century avian ancestor. Mol
Biol Evol 1990;7:194-200.
10. Hinshaw VS, Webster RG. The natural history of influenza A viruses.
In: Beare AS, editor. Basic and applied influenza research. Boca Raton
(FL): CRC Press; 1982. p. 79-104.
11. Scholtissek C, Naylor E. Fish farming and influenza pandemics. Nature
1988;331:215.
12. Bean WJ, Kawaoka Y, Wood JM, Pearson JE, Webster RG. Characterization
of virulent and avirulent A/Chicken/Pennsylvania/83 influenza A
viruses: potential role of defective interfering RNAs in nature. J
Virol 1985;54:151-60.
13. Senne DA, Pearson JE, Panigrahy B. Live poultry markets: a missing
link in the epidemiology of avian influenza. In: Proceedings of the
3rd International Symposium on Avian Influenza; 1997 27-29 May; The
Wisconsin Center, The University of Wisconsin-Madison. p. 50-8.
14. De Jong JC, Claas ECJ, Osterhaus ADME, Webster RG, Lim WL. A
pandemic warning. Nature 1997;389:554.
15. Subbarao K, Klimov A, Katz J, Regnery H, Lim W, Hall H, et al.
Characterization of an Avian influenza A (H5N1) virus isolated from a
child with a fatal respiratory illness. Science 1998;279:393-6.
16. Claas ECJ, Osterhaus ADME, van Beek R, De Jong JC, Rimmelzwaan GF,
Senne DA, et al. Human influenza A H5N1 virus related to a highly
pathogenic avian influenza virus. Lancet 1998;351:472-7.
17. Schnurrenberger PR, Woods GT, Martin RJ. Serologic evidence of human
infection with swine influenza virus. Am Rev Respir Dis
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Resurgent Vector-Borne Diseases as a Global Health Problem
Duane J. Gubler
Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
---------------------------------------------------------------------------
Vector-borne infectious diseases are emerging or resurging as a
result of changes in public health policy, insecticide and drug
resistance, shift in emphasis from prevention to emergency
response, demographic and societal changes, and genetic changes
in pathogens. Effective prevention strategies can reverse this
trend. Research on vaccines, environmentally safe insecticides,
alternative approaches to vector control, and training programs
for health-care workers are needed.
In the 120 years since arthropods were shown to transmit human disease,
hundreds of viruses, bacteria, protozoa, and helminths have been found to
require a hematophagous (blood-sucking) arthropod for transmission between
vertebrate hosts (1). Historically, malaria, dengue, yellow fever, plague,
filariasis, louse-borne typhus, trypanosomiasis, leishmaniasis, and other
vector-borne diseases were responsible for more human disease and death in
the 17th through the early 20th centuries than all other causes combined
(1). During the 19th and 20th centuries, vector-borne diseases prevented
the development of large areas of the tropics, especially in Africa; it was
not until these diseases were controlled that engineering feats such as the
Panama Canal could be completed (1,2).
Not long after the 1877 discovery that mosquitoes transmitted filariasis
from human to human, malaria (1898), yellow fever (1900), and dengue (1903)
were shown to have similar transmission cycles (2). By 1910, other major
vector-borne diseases such as African sleeping sickness, plague, Rocky
Mountain spotted fever, relapsing fever, Chagas disease, sandfly fever, and
louse-borne typhus had all been shown to require a blood-sucking arthropod
vector for transmission to humans (2).
Prevention and control programs were soon based on controlling the
arthropod vector. Yellow fever in Cuba was the first vector-borne disease
to be effectively controlled in this manner, followed quickly by yellow
fever and malaria in Panama. Over the next 50 years, most of the important
vector-borne public health problems were effectively controlled (Table 1).
Most of these programs established vertically structured vector control
organizations that emphasized elimination of arthropod breeding sites
(source reduction) through environmental hygiene along with limited use of
chemical insecticides. By the 1960s, vector-borne diseases were no longer
considered major public health problems outside Africa. Urban yellow fever
and dengue, both transmitted by Aedes aegypti, were effectively controlled
in Central and South America and eliminated from North America; malaria was
nearly eradicated in the Americas, the Pacific Islands, and Asia. The
discovery and effective use of residual insecticides in the 1940s, 1950s,
and 1960s contributed greatly to these successes.
Table 1. Successful vector-borne disease control/elimination
programs
-------------------------------------------------------------
Disease Location Year
-------------------------------------------------------------
Yellow fever Cuba 1900-1901
Yellow fever Panama 1904
Yellow fever Brazil 1932
Anopheles gambiae Brazil 1938
infestation
An. gambiae Egypt 1938
infestation
Louse-borne typhus Italy 1942
Malaria Sardinia 1946
Yellow fever
(Aedes aegypti) Americas 1947-1970
Malaria Americas 1954-1975
Malaria Global 1955-1975
Yellow fever West Africa 1950-1970
Onchocerciasis West Africa 1974-present
Bancroftian
filariasis South Pacific 1970s
Chagas disease South America 1991-present
-------------------------------------------------------------
However, the benefits of vector-borne disease control programs were
short-lived. A number of vector-borne diseases began to reemerge in the
1970s, a resurgence that has greatly intensified in the past 20 years
(3-7). Although the reasons for the failure of these programs are complex
and not well understood, two factors played important roles: 1) the
diversion of financial support and subsequent loss of public health
infrastructure and 2) reliance on quick-fix solutions such as insecticides
and drugs.
The Global Emergence/Resurgence of Vector-Borne Diseases
Evidence of the reemergence of vector-borne diseases such as malaria and
dengue was first observed in the 1970s in Asia and the Americas (5-9).
Warnings, however, were largely ignored until recently (10), and now it may
be difficult to reverse the trend.
Figure 1 shows some vector-borne parasitic, bacterial, and viral diseases
that have caused epidemics in the 1990s. While malaria is the most
important vector-borne disease because of its global distribution, the
numbers of people affected, and the large number of deaths, the
vector-borne viruses (arboviruses) are clearly the most numerous.
[fig]
Figure 1. Epidemic vector-borne diseases, 1990-1997. A. parasitic diseases,
B. parasitic diseases, C. arboviral diseases.
Malaria
The resurgence of malaria in Asia in the late 1960s and early 1970s
provides a dramatic example of how quickly vector-borne disease trends can
change. Malaria, transmitted to humans by anopheline mosquitoes, had been
nearly eliminated in Sri Lanka in the 1960s, with only 31 and 17 cases
reported in 1962 and 1963, respectively. By 1967, 3,468 cases were
reported. In 1968, however, a major epidemic caused 440,644 cases. In 1969,
537,705 cases were reported (Figure 2a); the disease has never been
effectively controlled since then. In India, a similar resurgence of
malaria occurred (Figure 2b), with sporadic outbreaks of disease beginning
in the early 1970s and nearly seven million cases by 1976. Sri Lanka and
India are classic examples of the lack of sustainability of vertically
structured prevention/control/elimination programs. Complacency, dwindling
financial and political support, and a change in strategy from vector
control to case finding and drug treatment were mainly responsible for the
resurgence of malaria in these countries.
More recently, vivax malaria has reemerged in Korea (Figure 2c). Urban
malaria in the Indian subcontinent and in parts of South America (Figure
2d) is also a major concern. In 1998, malaria is the most important
tropical disease with more than half of the world's population living in
areas of risk and with an estimated 200 million cases and two million
deaths each year (11). Widespread drug resistance of the parasites and
insecticide resistance among anopheline mosquito vectors have complicated
malaria control (4).
Malaria is the most common imported disease in the United States, where
anopheline mosquito vectors still exist (12). Approximately 1,000 suspected
malaria cases are imported into the United States each year, associated
with increased frequency of autochthonous cases; since 1987, 16 incidents
of autochthonous malaria have occurred in nearly all parts of the United
States. In each incident, however, transmission was limited to only a few
cases (12).
[fig]
Figure 2. The resurgence of malaria. A. Sri Lanka (data from Tissa
Vitarana, Office of Science and Technology, Sri Lanka); B. India (data
from Shiv Lal, Directory, National Malaria Eradification Program, India);
C. Korea (data from Dan Strickman, Walter Reed Army Institute of Research;
D. Manaus, Brazil (data from Bedsy Dutary, National Institute of Research
of the Amazon).
African Trypanosomiasis
Historically, African sleeping sickness, transmitted by the tsetse fly, has
been a major impediment to the social and economic development of Central
and East Africa. With the use of modern drugs, insecticides, and other
control methods, this disease was effectively controlled in most countries
by the mid-1960s. In the past 20 years, however, major epidemics have
occurred in East and Central Africa, mainly because control programs were
disrupted by war (13). In the Sudan, the Republic of Congo, and Angola,
which have high prevalence, poor surveillance, no drugs, and no vector
control, the disease poses a major public health threat. Although
available, some new drugs, vector control approaches, and diagnostic tests
are not being used because of lack of funding support.
African sleeping sickness is a low-priority rural disease. Effective,
sustainable control is unlikely until traditional uses of land change and
socioeconomic conditions improve in rural Africa (13). The primary approach
to control is treatment with drugs that are expensive and not readily
available (11). To reverse this trend, an integrated sustainable control
program must be implemented, including effective surveillance for case
finding, a network of treatment centers with a supply of drugs, and vector
control using trapping techniques (13).
Lyme Disease
Lyme disease, a bacterial tick-borne infection, is caused by Borrelia
burgdorferi. Discovered in the United States in 1975, the disease has
continued to increase in incidence and geographic distribution since
national surveillance was initiated in 1982. At that time, 497 cases were
reported compared with 11,700 to 16,455 cases each year between 1994 and
1997 (Figure 3) (cumulative total cases reported more than 109,000) (14).
Lyme disease has a global distribution in the temperate regions. Because of
the multistage disease and chronic complications associated with B.
burgdorferi infection, Lyme disease has major public health and economic
effects.
[fig]
Figure 3. Reported cases of Lyme disease in the United States, 1982-1997.
Lyme disease is transmitted by Ixodes ricinus complex hard ticks. In the
United States, I. scapularis, the deer tick, is the vector in the eastern
and midwestern states, and I. pacificus is the vector in the far western
states. While human cases of apparent Lyme disease are reported from most
states and many enzootic cycles of B. burgdorferi occur throughout the
country, the public health importance of these cases is uncertain.
Approximately 90% of reported Lyme disease cases occur each year in the
Northeast (Connecticut, Maryland, Massachusetts, New Jersey, New York,
Pennsylvania, and Rhode Island), upper Midwest (Minnesota and Wisconsin),
and Northwest (California) (14).
Plague
Plague is the original emerging disease, having caused major pandemics; the
most recent (late 19th century) is believed to be responsible for the
current global distribution of the disease, which is spread by rats on
ships (15). Like many other vector-borne diseases, plague was controlled
with antibiotics, insecticides, and rat control in the latter half of the
20th century. The number of cases reported to the World Health Organization
decreased to an all-time low of 200 cases in 1981 (15). In recent years,
however, epidemic plague has resurged, most notably in Africa, with an
average of nearly 3,000 cases reported annually (approximately 65% from
Africa) (15).
The decrease in plague incidence from 1950 to 1980 was followed by
decreased financial support, lowered interest, and ultimately the
deterioration of surveillance systems. Many countries were no longer
capable of making a laboratory diagnosis of plague in the 1990s. For
example, in 1994 when an outbreak of plague occurred in Western India (16)
(which had reported its last case of plague in 1966), lack of laboratory
capacity for diagnosis led to confusion as to the cause of the outbreak and
panic within the population. An estimated 500,000 people fled Surat for
other major cities, some of which subsequently reported secondary plague
transmission (16).
Because effective epidemiologic investigation and an accurate laboratory
diagnosis were not made in time, a relatively unimportant, focal public
health event turned into an international public health emergency costing
the Indian and the global economies billions of U.S. dollars (17). Plague
can cause explosive epidemics when effective laboratory-based surveillance
and prevention and control are not maintained in countries with enzootic
disease. An important lesson learned from this incident was that
laboratory-based international infectious disease surveillance is
cost-effective.
Dengue
Dengue fever caused major epidemics from the 17th to the early 20th
centuries (18). In most Central and South American countries, effective
disease prevention was achieved by eliminating the principal epidemic
mosquito vector, A. aegypti, during the 1950s and 1960s. In Asia, however,
effective mosquito control was never achieved, and a severe hemorrhagic
fever (DHF) emerged following World War II. During the 1950s, 1960s, and
1970s, this new form of dengue occurred as periodic epidemics in a few
countries. During the 1980s, however, incidence increased dramatically,
expanding distribution of the virus and the mosquito vector to the Pacific
islands and tropical America (18). In the latter region, the Ae. aegypti
eradication program had been disbanded in the early 1970s; by the 1980s,
this species had reinfested most tropical countries of the region (Figure
4). Increased disease transmission and frequency of epidemics caused by
multiple virus serotypes in Asia increased the movement of dengue viruses
into these regions, resulting in a dramatic increase in epidemic dengue
fever; hyperendemicity (the cocirculation of multiple virus serotypes); and
the emergence of DHF in the Pacific Islands, the Caribbean, and Central and
South America. Thus, in less than 20 years, both the American tropics and
the Pacific Islands went from not having dengue to having an important
dengue/DHF problem in 1998.
[fig]
Figure 4. Geographic distribution of Aedes aegypti in the Americas,
1930s, 1970, and 1998.
Globally, DHF has emerged as a major cause of hospitalization and death.
The number of DHF cases reported from 1981 to 1995 is four times higher
than that of the previous 30 years. In 1998, more than 2.5 billion persons
live in areas of risk (Figure 5). Dengue is the second most important
tropical disease (after malaria) with approximately 50 to 100 million cases
of dengue fever and 500,000 cases of DHF each year.
[fig]
Figure 5. Global distribution of Aedes aegypti and of epidemic dengue,
1980-1998.
Because of limited surveillance data and gross underreporting in most
disease-endemic countries, the economic and public health impact of dengue
is greatly underestimated.
Yellow Fever
Like dengue fever, yellow fever caused major epidemics from the 17th to the
20th centuries and was effectively controlled in the Americas by the Ae.
aegypti elimination program in the 1950s and 1960s. Yellow fever is
maintained in forest cycles involving monkeys and canopy-dwelling
mosquitoes in both Africa and the Americas. Human infections since the
1950s have been primarily in persons associated with the forest. Since the
mid-1980s, however, epidemic yellow fever has resurged in West Africa, and
for the first time in history, an outbreak occurred in Kenya in 1992 to
1993 (19).
Although the last urban epidemic in the Americas was in 1942 (20), urban
epidemics may recur because nearly all major urban centers of the American
tropics have been reinfested by Ae. aegypti in the past 20 years. Most
persons in tropical American cities are at high risk for epidemic urban
transmission because of low yellow fever immunity. Of added concern are the
increasingly frequent reports of imported yellow fever to mosquito-infested
urban areas (Figure 6). In the past 2 years, yellow fever cases have been
imported to Santa Cruz, Bolivia; Manaus, Brazil; Villavicencia, Colombia;
and Iquitos, Peru, all urban centers infested with Ae. aegypti. Moreover,
two patients with yellow fever cases imported to the United States and
Switzerland died; neither patient had been vaccinated.
[fig]
Figure 6. Major urban centers of South America recently infested with Aedes
aegypti and at high risk for imported yellow fever.
Thus, the frequency of yellow fever moving from the American rain forest to
tropical urban areas is increasing, and it is likely only a matter of time
before an urban yellow fever epidemic will occur. The disease will then
likely spread rapidly to other cities in the Americas and from there to
cities in Asia and the Pacific, much as dengue has in the past 20 years
(18). Because of the similarities in clinical expression between yellow
fever and other common diseases such as dengue and leptospirosis and
because the surveillance systems needed to detect yellow fever are very
limited in most countries, widespread epidemic transmission would likely
occur before the disease is detected. Emergency methods of controlling Ae.
aegypti are ineffective (21,22); therefore, a major international public
health emergency could occur.
These are only a few examples of emergent/resurgent vector-borne diseases,
but there are many more that are causing increasingly frequent epidemics.
Many go unreported because laboratory-based surveillance systems are not
available in many countries.
Factors Involved in Vector-Borne Disease Emergence
The factors responsible for the emergence/resurgence of vector-borne
diseases are complex. They include insecticide and drug resistance, changes
in public health policy, emphasis on emergency response, deemphasis of
prevention programs, demographic and societal changes, and genetic changes
in pathogens (10). Public health policy decisions have greatly decreased
the resources for surveillance, prevention, and control of vector-borne
diseases in the 1960s and 1970s, primarily because control programs had
reduced the public health threat from these diseases. Those decisions, the
technical problems of insecticide and drug resistance, as well as too much
emphasis on insecticide sprays to kill adult mosquitoes, contributed
greatly to the resurgence of diseases such as malaria and dengue. Decreased
resources for infectious diseases in general resulted in the
discontinuation or merger of many programs and ultimately to the
deterioration of the public health infrastructure required to deal with
these diseases. Moreover, good training programs in vector-borne diseases
decreased dramatically after 1970. Thus, in 1998, we are faced with a
critical shortage of specialists trained to respond effectively to the
resurgence of vector-borne diseases (10,23). A related problem is the lack
of preventive medicine training in most medical schools. The curative
approach and emphasis on high-tech solutions to disease control have led
most physicians, health officials, and the public to rely on "magic
bullets" to cure an illness or control an epidemic (21).
Major global demographic and societal changes of the past 50 years have
directly affected the emergence/resurgence of vector-borne and other
infectious diseases (10,21,23,24). Unprecedented population growth, mostly
in developing countries, resulted in major movements of people, primarily
to urban centers. This unplanned and uncontrolled urbanization (inadequate
housing, deteriorating water, sewage, and waste management systems)
produced ideal conditions for increased transmission of mosquito-borne,
rodent-borne, and water-borne diseases. The prospects for the future are
not good; nearly all of the world's population growth in the next 25 years
will occur in the urban centers of developing countries, many of them in
tropical areas where vector-borne diseases occur most frequently (25).
Other societal changes, such as agricultural practices and deforestation
(10), increase the risk for vector-borne disease transmission (Table 2).
Many irrigation systems and dams have been built in the past 50 years
without regard to their effect on vector-borne diseases. Similarly,
tropical forests are being cleared at an increasing rate, and agricultural
practices such as rice production have also increased.
Table 2. Influences on emergent/resurgent vector-borne diseases
-------------------------------------------------------------------------------
Urbanization Deforestation Agricultural Practices
-------------------------------------------------------------------------------
Dengue fever Loaiasis Malaria
Malaria Onchocerciasis Japanese encephalitis
Yellow fever Malaria St. Louis encephalitis
Chickungunya Leishmaniasis West Nile fever
Epidemic polyarthritis Yellow fever Oropouche
West Nile fever Kyasanur Forest Western equine
St. Louis encephalitis disease encephalitis
Lyme disease La Crosse encephalitis Venezuelan equine
Ehrlichiosis Eastern equine encephalitis
Plague encephalitis
Lyme disease
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Consumer products make ideal breeding sites for domesticated mosquitoes.
Packaged in nonbiodegradable plastics, cellophanes, and tin, these products
tend to be discarded in the environment where they collect rainwater.
Discarded automobile tires, many in the domestic environment, make ideal
mosquito breeding places as well as rat and rodent harborages. Container
shipping and the global used tire industry have contributed to the
increased geographic distribution of selected mosquito species that lay
their eggs in used tires (26).
Finally, the jet airplane has had a major influence on global demographics
(27). The airplane provides the ideal mechanism for transporting pathogens
between population centers (10,18,21,23). The result is a constant movement
of viruses, bacteria, and parasites among cities, countries, regions, and
continents.
Climate change (e.g., global warming and El Niño Southern Oscillation) is
often cited as the cause for the emergence/resurgence of vector-borne
diseases, especially malaria, dengue, and yellow fever. While meteorologic
factors such as temperature, rainfall, and humidity influence the
transmission dynamics of vector-borne diseases, climate change has not yet
been scientifically proven to have caused the emergence/resurgence of any
of the vector-borne diseases described above.
The Future
Reversing the trend of emergent/resurgent vector-borne diseases is a major
challenge. Vaccines, available for only a few diseases (yellow fever,
Japanese encephalitis, tick-borne encephalitis, tularemia, plague), are not
widely used. Vaccine prospects for major vector-borne diseases are not
good. With the exception of malaria, few other vector-borne diseases have
funding for vaccine research.
In the next decade, therefore, vector control will be required to interrupt
transmission of most emergent/resurgent vector-borne diseases.
Environmentally safe insecticides and research on alternative approaches
(such as biological control) are needed. Integrated prevention strategies
must be developed and implemented in endemic/enzootic-disease areas. In
addition to economic support for research, human resources are needed to
develop and implement sustainable prevention programs. Adequately trained
personnel are lacking in most developing countries, as are academic
institutions with the programs to train them. Policy changes must be made
to support public health approaches to disease prevention. All these
factors are needed to rebuild the public health infrastructure. Ultimately,
however, demographic trends that have resulted in increased population
pressure on urban centers and changes in agricultural practices must be
reversed. Only then will we be able to effectively reverse the current
trend of emergent/resurgent vector-borne disease in the 21st century.
Acknowledgment
The author is grateful to numerous colleagues around the world for
contributing data and information used in preparation of this paper.
Dr. Gubler is director of the Division of Vector-Borne Infectious Diseases,
National Center for Infectious Diseases, CDC, in Fort Collins, Colorado.
His research interests include field epidemiology, laboratory diagnosis,
surveillance, prevention, and control of vector-borne diseases, with
special emphasis on dengue/dengue hemorrhagic fever and other arboviruses.
Address for correspondence: Duane J. Gubler, Division of Vector-Borne
Infectious Diseases, National Center for Infectious Diseases, Centers for
Disease Control and Prevention, P.O. Box 2087, Fort Collins, CO 80522, USA;
fax: 970-221-6476; e-mail: djg2@cdc.gov.
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Hunter tropical medicine, 7th edition. Philadelphia (PA): W. B.
Saunders; 1991. p. 981-1000.
2. Philip CB, Rozenboom LE. Medico-veterinary entomology: a generation of
progress. In: Smith RF, Mittler TE, Smith CN, editors. History of
entomology. Palo Alto (CA): Annual Reviews Inc; 1973.
3. Gubler DJ. The global resurgence of arboviral diseases. Trans Roy Soc
Trop Med Hyg 1996;90:449-51.
4. Krogstad DJ. Malaria as a reemerging disease. Epidemiol Rev
1996;18:77-89.
5. Bruce-Chwatt LJ. The Manson Oration, May 1979. Man against malaria:
conquest or defeat? Trans Roy Soc Trop Med Hyg 1979;73:605-17.
6. Hammon WM. Dengue hemorrhagic fever–do we know its cause? Am J Trop
Med Hyg 1973;22:81-91.
7. Pan American Health Organization. Dengue in the Caribbean, 1977.
Scientific Publication No. 375. Washington: The Organization; 1979.
8. Reeves WC. Recrudescence of arthropod-borne diseases in the Americas.
Washington: Pan American Health Organization; 1972. PAHO Scientific
Publication No. 238. DC.
9. Groot H. The reinvasion of Colombia by Aedes aegypti: aspects to
remember. Am J Trop Med Hyg 1980;29:330-8.
10. Lederberg J, Shope RE, Oaks SC Jr, editors. Emerging infections:
microbial threats to health in the United States. Washington: National
Academy Press; 1992.
11. The World Health Report 1996: fighting disease, fostering development.
Geneva: World Health Organization; 1996.
12. Zucker JR. Changing patterns of autochthonous malaria transmission in
the United States: a review of recent outbreaks. Emerg Infect Dis
1006;2:37-43.
13. Molyneux DH. Current public health status of the trypanosomiases and
leishmaniases. In: Hilde G, Mottram JC, Coombs GH, Holmes PH, editors.
Trypanosomiasis and leishmaniasis. London: CAB International; 1997. p.
39-50.
14. Dennis DT. 1998. Epidemiology, ecology, and prevention of Lyme
disease. In: Rahn DW, Evens J, editors. Lyme disease. Philadelphia
(PA): American College of Physicians; 1998. p. 7-34.
15. Dennis DT. Plague as an emerging disease. Emerging Infections II. In
press 1998.
16. Ramalingaswami V. The plague outbreaks of India, 1994–a prologue.
Current Science 1996;71:781-806.
17. Plague—India 1994: economic loss. Geneva: World Health Organization;
1997. p. 14.
18. Gubler DJ. Dengue and dengue hemorrhagic fever: its history and
resurgence as a global public health problem. In: Gubler DJ, Kuno G,
editors. Dengue and dengue hemorrhagic fever. London: CAB
International. p. 1-22.
19. Sanders EJ, Tukei PM. Yellow fever: an emerging threat for Kenya and
other East African countries. East Afr Med J 1996;73:10-2.
20. Monath TP. Yellow fever. In: Monath TP, editor. The arboviruses:
epidemiology and ecology. Boca Raton (FL): CRC Press; 1988. p.
139-231.
21. Gubler DJ. Aedes aegypti and Aedes aegypti-borne disease control in
the 1990s: top down or bottom up. Am J Trop Med Hyg 1989;40:571-8.
22. Reiter P, Gubler DJ. Surveillance and control of urban dengue vectors.
In: Gubler DJ, Kuno G, editors. Dengue and dengue hemorrhagic fever.
London: CAB International; 1997. p. 425-62.
23. Gubler DJ. Epidemic dengue and dengue hemorrhagic fever: a global
public health problem in the 21st century. In: Scheld WM, Armstrong D,
Hughes JM editors. Emerging infections 1. Washington: ASM Press; 1997.
p. 1-14.
24. Addressing emerging infectious disease threats: a prevention strategy
for the United States. Atlanta (GA): Centers for Disease Control and
Prevention; 1994.
25. World resources 1996-97. A guide to the global environment. The urban
environment. New York: Oxford University Press: 1996.
26. Reiter P, Sprenger D. The used tire trade: a mechanism for the
worldwide dispersal of container breeding mosquitoes. J Am Mosq Ctrl
Assoc 1987;3:494-501.
27. Gubler DJ. Arboviruses as imported disease agents: the need to
increased awareness. Arch Virol 1996;11:21-32.
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Global Climate Change and Infectious Diseases
R. Colwell,* P. Epstein,† D. Gubler,‡ M. Hall,§ P. Reiter,‡ J. Shukla¶, W.
Sprigg,# E. Takafuji,** and J. Trtanj§
*University of Maryland Biotechnology Institute, College Park, Maryland,
USA; †Harvard Medical School, Boston, Massachusetts, USA; ‡Centers
for Disease Control and Prevention, Atlanta, Georgia, USA; §National
Oceanic and Atmospheric Administration, Washington, D.C., USA; ¶Institute
of Global Environment and Society, Inc., Calverton, Maryland, USA;
#National Research Council, Washington, D.C., USA; **Walter Reed Army
Institute of Research, Washington, D.C., USA
---------------------------------------------------------------------------
Climate change, if it occurs at the level projected by current global
circulation models, may have important and far-reaching effects on
infectious diseases, especially those transmitted by poikilothermic
arthropods such as mosquitoes and ticks. Although most scientists agree
that global climate change will influence infectious disease transmission
dynamics, the extent of the influence is uncertain. This conference session
provided an overview of the issues associated with climate change as it
relates to the emergence and spread of infectious diseases.
[photo]
Two papers set the stage by reviewing data that support or do not support the
conclusion that climate change has already influenced transmission of infectious
diseases. Some studies support such conclusions as warming at higher elevations,
including the retreat of tropical summit glaciers, upward plant displacement,
elevational shifts in insect populations and vector-borne diseases, and upward
shift of the freezing isotherm (150 m, which is equivalent to 1°C warming) since
1970. Other studies, however, point out that in centuries past, vector-borne
diseases such as malaria, dengue, and yellow fever occurred regularly in
temperate regions in epidemic form during the summer months. The diseases were
eliminated from Europe and North America, and although many areas still have
the mosquito vectors, epidemic disease transmission has been prevented by
improved living conditions and effective mosquito control. Also, since malaria
has historically occurred at elevations of 2,400 m to 2,600 m, its current
transmission at high altitudes does not necessarily prove that transmission at
these high altitudes is the result of climate change.
The second set of papers provided current evidence of global climate change
and described how climatologic data might be used to understand geographic
spread and transmission dynamics of an important emerging infectious
disease such as cholera. The speakers concluded that global warming is
occurring and that weather events appear to be associated with the
emergence and spread of cholera in the Americas between 1991 and 1998.
Speakers then focused on the research that will be required to answer the
many questions relating to climate change and infectious diseases. They
described an effort initiated by the National Oceanic and Atmospheric
Administration to take advantage of the strong El Niño Southern Oscillation
(ENSO) signal in 1997 to 1998 to study the effect of ENSO on vector-borne
diseases. The hypothesis was that ENSO-related changes in precipitation,
temperature, and other environmental variables have both direct effects
(through drought, flood, and extreme weather events) and indirect effects
(through changes in transmission and outbreaks of infectious diseases,
particularly diseases transmitted by mosquitoes, rodents, or water) on
human health. Diseases studied in the ENSO experiment include cholera in
Bangladesh and Peru, cryptosporidiosis in the United States, water-borne
and water-related diseases in Florida, marine ecologic disturbances in the
eastern United States, dengue in different parts of the world, malaria in
Africa, domestic arboviral encephalitides in the United States, and
hantavirus pulmonary syndrome in the United States. The National Academy of
Sciences and Institute of Medicine plan to appoint a committee to review
critically the published work on this topic and make recommendations for a
national research agenda. A number of U.S. government agencies will support
this committee financially.
The final presentation addressed the need for cooperation and partnerships
in implementing this research agenda. The government agencies involved have
unique expertise and perspectives that can be brought to bear on the
problem of climate change. Emphasis must be placed on public health
intervention measures that are properly implemented and can mitigate the
effect of global climate change on infectious disease incidence and
geographic spread.
Suggested Bibliography
1. Epstein PR, Diaz HF, Elias S, Grabherr G, Graham NE, Martens WJM, et
al. Biological and physical signs of climate change: focus on
mosquito-borne disease. Bulletin of the American Meteorological
Society 1998;78:409-17.
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Emerging Zoonoses
James Childs,* Robert E. Shope,† Durland Fish,‡ Francois X. Meslin,§
Clarence J. Peters,* Karl Johnson,¶ Emilio Debess,# David Dennis,* and
Suzanne Jenkins**
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA;
†University of Texas Medical Branch at Galveston, Galveston, Texas, USA;
‡Yale School of Medicine, New Haven, Connecticut, USA; §World Health
Organization, Geneva, Switzerland; ¶University of New Mexico, Albuquerque,
New Mexico, USA; #National Association of Public Health Veterinarians; and
**Council of State and Territorial Epidemiologists
---------------------------------------------------------------------------
Zoonotic pathogens cause infections in animals and are also transmissible
to humans; knowledge of the extrahuman reservoirs of these pathogens is
thus essential for understanding the epidemiology and potential control of
human disease. Zoonotic diseases are typically endemic and occur in natural
foci. However, ecologic change and meteorologic or climatic events can
promote epidemic expansion of host and geographic range. For practical
reasons, surveillance of zoonotic agents too often relies on the
identification of human cases. Surveillance in natural hosts may be
difficult because of the ecologic complexity of zoonoses; multidisciplinary
teams of ecologists, mammalogists, ornithologists, and entomologists, as
well as physicians and epidemiologists, may be required for successful
investigations. A recent trend in studying zoonoses that have strong
environmental correlates includes geographers and mathematical modelers,
who integrate satellite remote sensing and geographic information systems
to predict outbreaks. Understanding extrahuman life cycles and predicting
zoonotic disease outbreaks may permit control activities targeted at
several points in the cycle of pathogen maintenance before human infection
begins. These control efforts are important because most zoonoses are not
amenable to eradication, except perhaps those in areas where animal
reservoirs are targeted for vaccination, e.g., fox rabies in Europe.
In the United States, tick-borne zoonoses have emerged at the relatively
constant rate of one per decade over the past 100 years. However, the
incidence of human tick-borne disease has increased exponentially over the
past two decades—primarily because of ecologic change caused by
reforestation. Large-scale reforestation of the northeastern coastal states
since the early part of this century precipitated a natural succession of
ecologic changes that included increased deer density, expansion of the
natural range of the deer-dependent tick Ixodes scapularis, and increased
transmission rates of tick-borne pathogens. I. scapularis is a competent
vector of at least four enzootic tick-borne pathogens (Borrelia
burgdorferi, Babesia microti, Ehrlichia phagocytophila, and a Powassanlike
encephalitis virus). Because of its anthropophilic nature, I. scapularis is
also an excellent bridge vector for transmission of these pathogens to
humans. This dramatic expansion in the distribution of I. scapularis in the
northeastern United States has caused the current epidemic of Lyme disease
and has increased the range of human babesiosis in New England. However,
the recent emergence of human granulocytic ehrlichiosis resulted from the
recognition of human cases caused by a zoonosis already well established
within I. scapularis populations. As I. scapularis continues to expand its
range bringing more people in contact with novel enzootic tick-borne
pathogens, additional tick-borne diseases may emerge as new public health
threats.
Since the unprecedented impact of bovine spongiform encephalopathy (BSE)
and new variant Creutzfeldt-Jakob disease (nvCJD) on animal health and
national politics and economies, this new zoonosis has prompted many
questions in the field of foodborne disease control and prevention. BSE and
nvCJD, caused by an unconventional agent, the nature of which remains
controversial, are invariably fatal. The threat to human health is
compounded because the causative agent is resistant to conventional
physical and chemical methods of decontamination and cannot be fully
inactivated by any of the current food technologies. A preclinical
diagnostic test remains elusive. Traditional food safety programs cannot
prevent infection to consumers once the agent has entered the food chain.
New and reemerging conventional or unconventional foodborne pathogens of
animal origin must be better addressed, and food safety programs with
emphasis on the preharvest and harvest food stages must be developed.
Control is best achieved at the feed preparation and farm level and at the
harvest stage. Consumer health takes precedence over market concerns, and
when data are incomplete, a conservative response is warranted until the
risk can be accurately assessed.
Diseases of humans caused by rodent-borne viruses in the families
Bunyaviridae and Arenaviridae include the newly recognized hantavirus
pulmonary syndrome and the South American hemorrhagic fevers. Many of these
diseases present control challenges—because vaccines may not be developed,
because of characteristics of the exposed population, or because control of
rodent reservoirs in the affected areas is impractical or unachievable.
Many of these diseases may be increasing in frequency as humans modify
forest and natural savannah environments for agriculture, inadvertently
promoting human-rodent contact and increasing the number of suitable
habitats used by rodents, which are habitat generalists and also virus
reservoirs. Serious gaps in our understanding of the natural history of
these viruses and their hosts limit a targeted intervention. The prevalence
of virus infection in rodent populations may be less important than the
absolute number and demographic characteristics of infected mice. A single,
newly infected, subadult mouse may shed in its urine and feces the high
quantities of virus needed to infect a person by the aerosol route.
However, effective maintenance of virus may hinge on persistent infections
in older, dominant, male rodents that survive over extended periods and
have the highest prevalence ofinfection but only shed sufficient virus in
their saliva to perpetuate rodent-t o-rodent transmission through
intraspecific aggressive encounters. Recent developments in remote sensing
and geographic information systems, coupled with longitudinal studies of
virus activity and rodent population dynamics, hold promise for developing
models predictive of when and where outbreaks of rodent-borne zoonoses
could occur.
Surveillance of the unknown appears to be a thankless task, and it is
probable that we will learn of an "Andromeda" event after an urban
population is struck, although the agent is most likely to arise in a
rural, tropical setting. The health and safety of future generations may
depend on our ability to rapidly detect, monitor, and control disease
caused by novel zoonotic agents. Uniform surveillance definitions, reliable
specimen collection, shipping and handling, and means for rapid
communication will be critical.
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New Approaches to Surveillance and Control of Emerging Foodborne Infectious
Diseases
Robert V. Tauxe
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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Each year in the United States, foodborne diseases affect millions of
persons, who become ill after exposure to any of a growing spectrum of
identified agents and toxins. Typhoid fever and other foodborne diseases
common a century ago have been controlled by measures that prevent
contamination of food and water with human sewage and by technologies (such
as milk pasteurization) that eliminate any remaining pathogens. Many
recently identified foodborne diseases are caused by contamination with
animal feces and can be prevented by measures that reduce contamination and
eliminate residual pathogens. In the future, growing attention will need to
be directed to the safety of the food and water the animals themselves
consume.
New foodborne diseases emerge for many reasons, including changes in the
pathogens themselves, increasingly centralized and concentrated food
production, globalization of the food supply, and increases in populations
at higher risk. Better surveillance and investigation now detect outbreaks
that a few years ago would have been missed. The continuing challenges are
to identify new pathogens as they emerge, understand how foodborne
pathogens contaminate food and cause illness, and define and implement the
best prevention strategies.
Many efforts are now under way to improve food safety in the United States.
In 1997, the National Food Safety Initiative outlined an interagency effort
to enhance foodborne disease surveillance, research, and prevention. The
Centers for Disease Control and Prevention (CDC) and state and local health
departments have begun to implement improved surveillance strategies,
including additional resources for basic surveillance and investigation, an
active surveillance network called FoodNet, surveillance for antimicrobial
resistance, and a network for molecular subtyping called PulseNet. Basic
research at the National Institutes of Health (NIH) is clarifying virulence
mechanisms and developing prevention tools. Dennis Lang, National Institute
of Allergy and Infectious Diseases, emphasized that NIH-supported
investigators who study the organisms responsible for foodborne illness
represent a national resource that can be used to address food safety
questions more effectively. New approaches to prevention are now being
implemented by the food regulatory agencies, and more approaches, including
irradiation, have been approved for industry use.
Barbara Herwaldt, CDC, reported that Cyclospora cayetanensis is an
archetypical emerging foodborne pathogen. This recently described parasitic
pathogen sprang to national attention in nationwide outbreaks in 1996,
which were traced to raspberries imported from Guatemala. Outbreaks
recurred in 1997, leading to a suspension of importation, despite efforts
of the Guatemalan raspberry industry to reduce potential contamination.
With improved surveillance, other outbreaks were detected, investigated,
and traced to mesclun lettuce and basil. CDC investigation has now
documented C. cayetanensis as a common cause of springtime diarrhea among
children in Guatemala. Critical gaps in our understanding of the biology
and epidemiology of this parasite, particularly in the raspberry farm
environment, need to be closed before effective control measures can be
developed.
B. Swaminathan, CDC, described a new subtyping strategy for public health
surveillance of Escherichia coli O157:H7 that will become available
electronically later this year. This strategy depends on standardized
molecular fingerprinting in public health and food regulatory agency
laboratories by pulsed-field gel electrophoresis (PFGE). With standardized
methods and equipment, excellent interlaboratory comparability of DNA
fingerprint patterns has been achieved. Twenty-four states, the U.S.
Department of Agriculture, and the Food and Drug Administration are now
equipped to use CDC's PFGE method for E. coli O157:H7. These laboratories
are being linked to form a collaborative network for molecular subtyping,
PulseNet, which will permit rapid comparison of identified PFGE profiles
with the national database at CDC. Efforts are also under way to apply the
same strategy to other foodborne pathogens. In 1997, PFGE results were
already critical to epidemiologic investigations of several outbreaks of E.
coli O157:H7 infections. These included a Colorado outbreak traced to
ground beef and a multistate outbreak related to alfalfa sprouts.
Alison O'Brien, Uniformed Services University of the Health Sciences,
described a new approach to prevention, based on an attachment protein
present in enteropathogenic E. coli as well as E. coli O157:H7. This
protein, intimin, permits the bacteria to attach to mucosal cells and
produce a characteristic pathologic change. In a calf model, E. coli
O157:H7 can cause diarrhea and this change; the change does not occur if
the E. coli lack the gene for intimin. Intimin is highly antigenic and acid
stable, and antibodies raised to it block adherence in vitro. The intimin
gene has been introduced into plants, where it is produced in the leaves.
This means that an antitransmission vaccine based on intimin can be
produced cheaply in plants and be given to calves. The vaccine could even
be fed to animals if intimin were produced in fodder plants. In the future,
we may be able to prevent E. coli O157:H7 in humans by vaccinating the
bovine reservoir.
Henrik Wegener, Danish Zoonosis Center, described the emergence of
vancomycin-resistant enterococci (VRE) in northern Europe, linking it to
the use of a related glycopeptide antibiotic, avoparsin, in food animals.
VRE were common in poultry flocks and swine herds exposed to this
antibiotic, and 5% of healthy carnivorous humans were carriers of VRE.
Sequencing the resistance gene showed that one genotype was present in
poultry, a second was present in swine, and both were present in humans.
Thus, VRE are unlikely to have spread from animals to humans rather than
vice versa. After avoparsin was withdrawn in Denmark in 1995, the
prevalence of VRE in chickens dropped; the European Union banned the agent
in 1997. In some countries, amplification of VRE in hospitals where
vancomycin use is frequent may follow introduction of resistance strains
from food sources. Other antibiotics being developed for human use (e.g.,
streptogramins) have analogues used in agriculture for years, to which
resistance may already have emerged. Integrated resistance surveillance
systems, data on antibiotic use in humans and in agriculture, and prudent
agricultural use policies are critical to managing the growing challenge of
antibiotic resistance related to foods and food animals.
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FoodNet and Enter-net: Emerging Surveillance Programs for Foodborne
Diseases
Samantha Yang
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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The public health challenges of foodborne diseases are changing as a result
of newly identified pathogens and vehicles of transmission, changes in food
production and distribution, and an apparent decline in food safety
awareness. Response to these new challenges requires new surveillance
strategies to monitor the incidence of human illness and provide data for
developing effective prevention strategies.
FoodNet
The Foodborne Diseases Active Surveillance Network (FoodNet), the principal
foodborne disease component of the Centers for Disease Control and
Prevention's (CDC) Emerging Infections Program (EIP), is a collaborative
project with participating EIP sites, the U.S. Department of Agriculture
(USDA), and the U.S. Food and Drug Administration (FDA). To determine more
precisely the incidence of foodborne illness in the United States, FoodNet
was established in five locations (selected counties in California,
Connecticut, and Georgia, and the entire states of Minnesota and Oregon) in
1995 and was expanded to selected counties in Maryland and New York in
1997. The population of these seven FoodNet sites in 1997 was 20.3 million
(7.7% of the U.S. population).
The objectives of FoodNet are to 1) describe the epidemiology of new and
emerging bacterial, parasitic, and viral foodborne diseases of national
importance; 2) more precisely determine the frequency and severity of
foodborne diseases in the United States; and 3) determine the proportion of
foodborne disease caused by eating specific foods. By monitoring foodborne
disease incidence over time, FoodNet will document the effectiveness of new
food safety initiatives, such as the USDA Food and Safety Inspection
Service's Pathogen Reduction and Hazard Analysis and Critical Control
Points (HACCP) Rule, in decreasing the number of cases of foodborne disease
in the United States each year. To address these objectives, FoodNet
conducts active surveillance and related studies: a population survey, a
physician survey, and a case-control study of Escherichia coli O157:H7
infections.
Population Survey
Duc Vugia, California Department of Health, reported the results of the
FoodNet population survey, which was conducted between July 1, 1996, and
June 30, 1997, in selected counties of California, Connecticut, Georgia,
and the entire states of Minnesota and Oregon. This survey provided an
estimate of the prevalence of acute diarrhea and the frequency with which
patients with acute diarrhea sought medical care. In 9,003 interviews, 11%
of persons reported acute diarrhea in the 4 weeks before the interview, 12%
of persons with acute diarrhea called a health-care provider as a result of
this illness, and 8% sought medical care. These data indicate an estimated
1.4 acute diarrheal episodes per person each year in the United States,
with 1% of the population seeking medical care because of acute diarrhea.
Physician Survey
In 1996, to obtain information on stool culturing practices, physicians in
California, Connecticut, Georgia, Minnesota, and Oregon were surveyed.
Results were reported by Thomas Hennessy, CDC. Of the 1,783 physicians
responding to this survey, 44% reported requesting a stool culture from the
most recent patient they remembered seeing who had acute diarrhea. Patient
factors significantly associated with stool culture requests included
bloody stools, a diagnosis of AIDS, diarrhea lasting longer than 3 days,
travel to a developing country, and fever. Stool culture ordering practices
differed by physicians' specialties and geographic site; however, culturing
practices did not differ by payment plan, such as managed care or
fee-for-service. Variability in culturing practices by specialty and
geographic location suggests a need for clinical diagnostic guidelines for
diarrheal illnesses.
Case-Control Study
A case-control study was conducted at FoodNet sites to identify risk
factors for sporadic E. coli O157:H7 infections and to explain variations
in the incidence of E. coli O157:H7 incidence among FoodNet sites. Heidi
Kassenborg, Minnesota Department of Health, presented results from this
study, which was conducted between March 1, 1996, and April 30, 1997, in
selected counties of California, Connecticut, Georgia, and the entire
states of Minnesota and Oregon. Data were obtained from 200 nonoutbreak
case-patients and 380 controls, matched by age and telephone exchange. For
all sites combined, illness was associated with eating pink hamburgers or
pink ground beef and with visiting a farm. Regional variation in beef
processing and in exposure to farms may have contributed to the regional
variability of E. coli O157:H7 infections.
Enter-net
Funded by the European Commission, Enter-net (formerly Salm-Net) is an
international surveillance system for Salmonella infections
(including data on antibiotic resistance) and E. coli O157 infections.
Microbiologists and epidemiologists responsible for national
laboratory-based surveillance of these pathogens in 15 European countries
form the Enter-net network. Ian Fisher, Communicable Disease Control
Centre, United Kingdom, described Enter-net and highlighted international
outbreaks recognized by the network. Investigations of these outbreaks led
to public health interventions and product recalls in Europe. The
international database of laboratory-confirmed cases of salmonellosis
produced by Enter-net also allows trends in this illness to be observed
over several years. For example, Enter-net is documenting the continuing
problem of Salmonella serotype Enteriditis in western Europe. Enter-net
represents a working model of how focused infection-specific international
surveillance involving key public health professionals can help monitor and
detect international outbreaks of foodborne infection.
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Enhancing State Epidemiology and Laboratory Capacity for Infectious
Diseases
Deborah A. Deppe
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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The Epidemiology and Laboratory Cooperative is an agreement that provides
state and large local health departments with resources to strengthen and
enhance basic capacity for public health surveillance and response for
infectious diseases. The funding is used to implement new technology,
upgrade systems, train staff, and purchase office and laboratory equipment.
Six of the 30 sites reported on their programs.
The Vermont Department of Health has undertaken statewide efforts to
improve communicable disease reporting through legislation. Before 1997,
public health law required physicians, nurses, hospital administrators, and
school and town health officials to report communicable disease (defined by
regulation) to the Commissioner of Health. Legislation proposed and passed
in 1997 required health maintenance organizations and managed care
organizations to report as well. This model law defines such information as
"confidential and privileged" and extends protection to investigations and
studies of disease outbreaks.
The Kansas Department of Health and Environment is building epidemiology
and laboratory capacity by expanding electronic surveillance and analysis,
enhancing surveillance for diarrheal disease, and integrating information
from other sources into the existing surveillance system. The new programs
are flexible so they can meet the challenges posed by new and emerging
infectious diseases as well as changing needs within public health.
The New York State Department of Health uses electronic communications to
enhance rapid reporting of communicable disease epidemiologic and
laboratory data within the state. In July 1997, seven counties began pilot
testing the New York Health Information Network (HIN), a secure Intranet
site. Web forms were designed for designated county personnel to submit
confidential case and supplemental information on 61 reportable
communicable diseases on the HIN. Since implementation, reports from local
health departments to the state have been more timely. Counties can easily
update and query their own data and can access statewide reports generated
by the state and posted on the HIN.
The Los Angeles County Department of Health Services has used pulsed-field
gel electrophoresis (PFGE) for outbreak investigations for 2 years.
Bacteria caused 140 (24%) of 576 reported outbreaks, 36% of health facility
outbreaks, but only 19% of community outbreaks. PFGE was used in 32
investigations, of which 29 (91%) were nosocomial. The most common
organisms were staphylococcus and enterococcus. In contrast, PFGE was used
in only 3 (4%) of 77 investigations of community bacterial outbreaks.
Health departments should consider the number, setting, and causes of
outbreaks that they investigate to determine if PFGE will be useful in
their investigation arsenal.
The Washington State Department of Health has developed a pilot electronic
laboratory-based reporting mechanism to route infectious disease reports
from a large managed care organization to local health agencies. The
overall goal is development of a generic electronic reporting mechanism.
For this project, Health Level 7 was identified as a common ground for
sharing data. Preliminary data suggest that timeliness and completeness of
reporting will improve. Adhering to nationally recognized standards and
codes may help reduce problems associated with transferring data; however,
no public health software or implementation package was available, so
resource-intensive customization was necessary.
The Maine Bureau of Health is attempting to characterize statewide
hepatitis C (HCV) prevalence through a review of existing databases
(hospital discharges, deaths, Medicaid registry, blood donor screening),
mandatory laboratory reporting with physician questionnaire follow-up, a
blinded seroprevalence survey in sexually transmitted disease clinics, and
a survey of gastroenterologists. Initial data indicate dramatic increases
in HCV-related hospitalization and in Medicaid expenditures during the
mid-1990s and an unexpectedly high proportion of patients with injection
drugassociated risk histories. Local surveillance data are useful for
public policy decisions and as educational tools for physicians and the
public.
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International Cooperation
James LeDuc
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
------------------------------------------------------------------------
Experts from the World Health Organization (WHO), the European Union (EU),
the U.S. Department of Defense (DoD), and other organizations summarized
existing and planned collaborations on emerging infectious diseases. The
session was chaired by David Heymann, WHO, and James LeDuc, CDC.
One speaker, V. Ramalingaswami, All India Institute of Medical Sciences,
India, summarized lessons learned from the plague outbreak in Surat, India.
The plague outbreak, the first in many years, found the country
ill-prepared to diagnose this disease, and young clinicians lacked
experience in recognizing or managing plague-infected patients.
Two speakers examined regional collaborations. Christopher Bartlett, Public
Health Laboratory Service, London, summarized the development of
international surveillance within EU. The Maastricht Treaty provided the
political will to underpin these activities; since the treaty, the heads of
European institutes with responsibility for national surveillance have met
regularly to assist in strategic development of surveillance activities.
Disease-specific networks have been established, each with an operational
protocol that sets out agreed case definitions and standard methods and use
of information obtained. High quality and timely information is now being
provided on a steadily increasing spectrum of infectious diseases through
weekly electronic and monthly surveillance bulletin publications. Oyewale
Tomori, regional virologist for Africa from WHO, explained that despite
substantial advances in disease prevention and control, communicable
diseases still constitute a major health problem for Africa. Concern about
the deplorable and worsening state of disease control in Africa has led
ministers of health in the region to pass several resolutions on prevention
of epidemic infectious diseases, yet frequent epidemics continue. Apart
from the development of a few disease-specific laboratory diagnostic
networks, laboratory services in Africa remain rudimentary and
underdeveloped. The WHO Regional Office for Africa has recently formulated
a strategic plan for integrated disease surveillance and an action plan to
strengthen laboratory capacity in Africa; international support is urgently
needed to implement these plans.
Global collaborations were also discussed. Nils Daulaire, U.S. Agency for
International Development (USAID), described the recently announced $50
million initiative to address infectious diseases globally. These funds
will be used to focus activities on tuberculosis, malaria, antimicrobial
resistance, and surveillance, both in countries with USAID missions, as
well as regionally. Michael McCarthy, DoD, summarized the new DoD
initiative on emerging infectious diseases and explained how the overseas
laboratories in Thailand, Kenya, Peru, Brazil, Egypt, and Indonesia will
work closely with their host nations and DoD scientists to address emerging
endemic disease threats. Maria Neira, WHO, described recent activities to
address cholera and other diarrheal diseases of epidemic potential
globally. These activities included the secondment of a CDC medical
epidemiologist to the WHO subregional office for southern Africa, where in
the past several years a plan to improve recognition and response to
epidemic diarrheal diseases has been developed and implemented. Included in
the program are training on improved patient management, strengthened
laboratory capacity, and better communication both within and between
countries of southern Africa.
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Public Health Surveillance and Information Technology
Robert W. Pinner
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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Applying Modern Information Technology to Reporting for Public Health the
Role of Standards
Clement McDonald, Indiana University School of Medicine, discussed the role
of standards in the application of modern information technology to public
health reporting. He pointed to the rich data sources stored electronically
in clinical laboratories, pathology and cytology reporting systems,
pharmacies, and hospitals, and emphasized the trend toward increasing
automation.
Interest and demand for electronic delivery of data come from many
interested parties—3rd party payers, researchers, physicians, and public
health officials. However, substantial barriers to smooth electronic flow
of this information include the storage of data in isolated areas, varying
internal structures among information systems, and considerable variation
in codes (e.g., for laboratory tests and results). Overcoming these
barriers requires defining, adopting, and implementing standards for
messages, codes, identification (e.g., persons, providers, places), and
security.
Messages
Health Level Seven (HL7) is a message standard that defines messages for
laboratory and other clinical results, immunization reporting, drug usages,
patient registration, and clinical trials. HL7 provides standards for the
structure and organization of clinical messages, defining data types, and
structure of the "records" in the message. A 1997 Healthcare Information
Management System Societies/Hewlett-Packard Leadership Survey found that
HL7 was the most important health informatics standard. HL7 is an American
National Standards Institute (ANSI)-approved clinical message standard used
widely in the United States and internationally. Additional information can
be found at the HL7 Internet web site:
http://www.mcis.duke.edu/standards/HL7/hl7.htm.
Codes
Code standards include Logical Observations Identifiers Names and Codes
(LOINC), a code standard that identifies clinical questions, variables, and
reports; Systematized Nomenclature of Medicine (SNOMED), which identifies
procedures and possible answers to these questions, such as test results;
Current Procedural Terminology, Version 4 (CPT4), which identifies
procedures; and the National Library of Medicine's Unified Medical Language
(UMLS), a metathesaurus of most code systems.
LOINC comprises a database of 15,000 variables with synonyms and
cross-mappings and covers a wide range of laboratory and clinical subject
areas (e.g., blood bank, chemistry, hematology, microbiology, vital signs,
body measurements, obstetric ultrasound, and electrocardiograms). LOINC's
formal naming structure has six parts: component (analyte), property
measured, time aspect, system (specimen, organ), precision, method. LOINC
is being adopted by several large reference laboratories, and it has been
incorporated into UMLS. Additional information about LOINC can be found at
http://www.mcis.duke.edu/standards/termcode/loinc.htm.
SNOMED defines code standards in a variety of clinical areas, called coding
axes: topography; morphology; function; living organisms; chemicals, drugs,
and biologic products; physical agents, activities, and forces;
occupations; social context; diseases/diagnoses; procedures; general
linkages/modifiers.
Security and Privacy
Privacy issues include both information technology and policy
considerations. For example, security can be addressed by encryption
techniques; policies that strongly discourage sharing of passwords are also
required for adequate privacy and security.
The public health system has been working to adopt needed standards for
immunization data transactions using HL7, data elements for emergency
department systems, and an approach for piloting electronic reporting from
clinical laboratories (which defines an HL7 message with LOINC codes for
identifying tests and SNOMED for identifying results, and a set of tables
that define reportable diseases in terms of specific tests and results)
(1).
The "rules" for achieving public health goals for electronic clinical data
are as follows. 1) Take advantage of the momentum of the existing standards
in hospitals and laboratories. 2) Recognize that this is difficult and will
take a long time. 3) Consider the source system data structures when
defining data needs.
Opportunities and Pitfalls for Surveillance
William Braithwaite, Department of Health and Human Services, described the
Administrative Simplification provision of the Health Insurance Portability
and Account Act of 1996 (HIPAA), which is intended to standardize the
electronic data interchange of certain administrative and financial
transactions while protecting the security and privacy of transmitted
information. The act mandates nine transaction standards (e.g., claims,
encounters, enrollment) including code sets; coordination of benefits
information; unique identifiers (including defining allowed uses) for
individuals, employers, health plans, and health-care providers; and
security, confidentiality, and electronic signatures. Once standards are
adopted, all health plans, clearinghouses, and those providers who choose
to conduct transactions electronically will be required to implement them.
The time line for implementation calls for adoption by the Secretary of
Health and Human Services (HHS) during 1998 of all standards except claim
attachments. ("Claim attachments" refers to information requested by an
insurance payer from a health-care provider to justify submitted charges
and is difficult to standardize because of the diversity of requests.) The
Secretary will look first to industry for a consensus standard developed by
an ANSI-accredited standards development organization and will rely upon
advice of the National Committee on Vital and Health Statistics. The HHS
implementation strategy involves a three-tiered approach. 1) The HHS Data
Council, a senior level policy guidance and decision-making group, is the
contact for the National Committee on Vital and Health Statistics. 2) The
Data Council's Health Data Standards Committee provides management of the
standards activities. 3) Implementation Teams provide research, analysis,
and development of standards and implementing regulations. The HHS adopts a
standard by publishing in the Federal Register a Notice of Intent to gather
information when no consensus exists and a Notice of Proposed Rule Making,
which provides a draft final rule. Publication of a Final Rule marks the
"adoption" by HHS of a particular standard.
Standards proposed for adoption include X12N Version 4010 for all
transactions except pharmacy claims, for which the National Council for
Prescription Drug Program Version 3.2 is proposed. Coding standards
proposed for adoption include ICD-9-CM, followed by ICD-10-CM in 2001 for
diagnoses, and ICD-9-CM Vol. 3 and Health Care Financing Administration
Common Procedure Coding System (HCPCS) for procedures. Proposed identifier
standards are the National Provider Identifier Health Care Financing
Administration (HCFA) for providers, the PAYERID (HCFA) for health plans;
and the Employer Identification Number (Internal Revenue Service) for
employers. A Notice of Intent will be published to seek input regarding the
individual identifier.
Important issues for public health surveillance in the next phases include
participating in development of the data content of these standards, the
standard for claim attachments, and the electronic medical records
standards, and developing health information privacy that maintains
appropriate access to data for public health purposes. Additional
information about the Administrative Simplification provisions of HIPAA can
be found at http://aspe.os.dhhs.gov/admnsimp/.
Public Health Surveillance for the 21st Century
Paul Stehr-Green, Washington Department of Health, emphasized public health
surveillance as the foundation of public health practice. Public health
surveillance needs to adapt to changing health practice, such as requiring
assessment of the risks for new and reemerging infectious diseases or
environmental hazards.
Public health should use the array of new information tools available. The
Blueprint for Surveillance is a document prepared by the Council of State
and Territorial Epidemiologists; it outlines the National Public Health
Surveillance System. This conceptual framework approaches surveillance for
not only reportable diseases, but also for a variety of health outcomes,
costs, and risk factors important to public health. The National Public
Health Surveillance System would involve other approaches (taking into
account available funding levels and the particular goals of surveillance
at each level of the public health system) in addition to the traditional
reportable diseases surveillance model. The primary goals of the National
Public Health Surveillance System include 1) coordinating new and existing
public health surveillance systems and linking them to facilitate the
exchange of data; 2) encouraging partnerships of federal, state, and local
public health professionals in decision-making about surveillance
activities; 3) reviewing existing surveillance (and other data collection
efforts that have a surveillance component) and making decisions about new
surveillance efforts and changes in existing systems; 4) monitoring the
adequacy of methods and processes involved in current surveillance systems;
and 5) developing a comprehensive description of conditions under
surveillance to bring attention to public health surveillance activities
and justify the need to support these activities. Recent accomplishments
include an effort coordinated by the Centers for Disease Control and
Prevention's (CDC) Health Information and Surveillance Systems Board to
integrate a number of current surveillance systems; updating the agency's
inventory of surveillance systems; developing a policy to monitor and
evaluate proposals to develop new or to substantially modify existing
surveillance systems; developing an investment analysis policy, which may
allow the use of some portion of funds to support the development and
maintenance of integrated surveillance and information systems by state
health departments; and developing resources that have been made available
to state health departments for enhancing infectious diseases surveillance
capacity. Washington State is formally reviewing the regulatory foundation
for surveillance and is developing and piloting electronic systems for the
collection, management, analysis, and dissemination of surveillance data
and information, including a collaboration between the health department
and Group Health Puget Sound Cooperative to electronically send selected
laboratory data to the department of health for surveillance. State and
local health departments should commit to changing from old to modern ways
of approaching surveillance, and CDC should provide leadership to bring
together disparate stakeholders and to provide flexible resources to help
state and local health departments effect modernization and integration of
surveillance.
Reference
1. McDonald CF, Overhage JM, Dexter P, Takesue BY, Dwyer DM. A framework
for capturing clinical data sets from computerized sources. Ann Intern
Med 1997;127:675-82.
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Innovative Information-Sharing Strategies
Bradford A. Kay,* Ralph J. Timperi,† Stephen S. Morse,‡ David Forslund,§
Julie J. McGowan,¶ and Thomas O'Brien#
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †The
Massachusetts State Laboratory Institute, Jamaica Plain, Massachusetts,
USA; ‡Defense Advanced Research Projects Agency, Arlington, Virginia, USA;
§Los Alamos National Laboratory, Los Alamos, New Mexico, USA; ¶University
of Vermont, Burlington, Vermont, USA; and #Brigham and Women's Hospital,
Boston, Massachusetts, USA
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National and global health issues accentuate the need for health
professionals to rapidly and effectively acquire and disseminate
information. This session highlighted four innovative systems for
communicating health information.
ProMED
Many experts, both within and outside government, have warned of the need
to improve capabilities for dealing with emerging infectious diseases;
development of an effective global infectious disease surveillance system
has been the primary recommendation. ProMED, a project of the Federation of
American Scientists, was inaugurated in 1993 at a conference in Geneva as a
vehicle for developing, coordinating, and promoting plans for a global
program to identify and respond to emerging infectious diseases. Members of
the ProMED Steering Committee include (among others) representatives of the
Centers for Disease Control and Prevention, the National Institutes of
Health, the World Health Organization (WHO), the Pan American Health
Organization, and the International Office of Epizootics.
In 1994, in cooperation with SatelLife/HealthNet, ProMED developed an
e-mail conference system, ProMED-mail, on the Internet. Originally
developed to allow worldwide scientist-to-scientist communications on
emerging infectious diseases, the system rapidly evolved into a prototype
for an open-architecture, real-time outbreak reporting system intended to
complement official surveillance systems. Today, with more than 10,000
subscribers from more than 125 countries, ProMED-mail is increasingly
providing the first reports of infectious disease outbreaks. All items are
read by scientists before posting. Reporting of incidents or outbreaks,
infectious disease problems of emerging interest, and discussions on how to
improve surveillance and response capabilities are especially encouraged.
To subscribe to the ProMED-mail electronic conference, send an e-mail
message to majordomo@usa.healthnet.org, and write "subscribe promed" in the
text space.
TeleMed
The Advanced Computing Laboratory at Los Alamos National Laboratory, Los
Alamos, New Mexico, developed TeleMed, an electronic medical record for
managing tuberculosis patients through a collaboration with the National
Jewish Center for Immunology and Respiratory Medicine in Denver, Colorado.
TeleMed provides a snapshot of patient data, presented chronologically with
access to laboratory test results, clinical history, radiology images,
reports, and treatment history. A particularly valuable feature allows
physicians to annotate the medical record, either orally or in writing, for
collaborating physicians to retrieve. Medical expertise can also be
exchanged in real time, with both users sharing the same screen and with
each having the capability to drive the mouse-pointer. TeleMed, now
available on the Internet using Java-based technology, enables physician
specialists to support primary care providers in the management of complex
medical problems. The technology creates a "virtual patient record" that
allows the integration of databases from multiple clinics and multiple
providers across geographically separated areas. This permits individual
health-care facilities to continue to own and manage their own data while
making the data accessible to others treating the same patient. TeleMed
provides a time-oriented record of the patient's medical history but only
retrieves the actual data on demand, thereby minimizing the bandwidth
requirements of the networking capabilities. Distributed ownership of the
data means that only one copy of the data exists, and that copy remains
where it was created. Location of the data is obtained from a master
patient index that provides pointers to the data. Security and access to
the data are controlled and protected with encryption technology.
VTMedNet
Vermont MedNet has been described as the "first comprehensive statewide
health information network in the nation." VTMedNet was developed to
provide timely access to medical information in support of health-care
delivery across the state of Vermont. The system was unique, not because it
used advanced technology, but because it used basic technology. VTMedNet
Plus, the network's evolution into voice, image, and video, has already
garnered national recognition for its initiatives in the area of
telemedicine. The network's home page has become a primary resource for the
dissemination of information about Vermont's health-care community and
information for Vermont's health-care consumer. It is also being used to
collect data for research and public health reporting and to distribute
aggregate information to improve health-care delivery in one of the
nation's most rural states. VTMedNet is the culmination of a partnership
among all major health-care organizations in Vermont, including the
University of Vermont, Fletcher Allen Health Care, Vermont State Medical
Society, and the Vermont Hospital Association. To access the network, users
must have their own computers and modems. A simple, configured, shareware
communications script is provided to those who request it. VTMedNet is
primarily an intranet and provides e-mail and Internet access for the
state's health-care providers and access to health information from around
the world. It is also designed to serve as a "virtual colleague,"
encouraging communication among all of Vermont's health-care providers
through targeted listservs.
WHONET
WHONET is database software for the management of routine microbiologic
test results. Its primary goals are to enhance local capabilities for
analysis and to facilitate the exchange of microbiologic data between
centers. WHONET is a DOS-based application that may be used alone on
personal computers or in conjunction with existing mainframe- or
minicomputer-based clinical information systems. Data conversion
("downloading" or "translating") from hospital systems or commercial
automated susceptibility test machines can usually be accomplished with
BACLINK software, also available free of charge from WHO. WHONET is not a
complete laboratory management system but can be used for simple clinical
reporting of results. Software development has concentrated on data
analysis, particularly of the results of antimicrobial susceptibility
tests. The analytic tools aid the selection of antimicrobial agents, the
identification of hospital outbreaks, and the recognition of quality
control problems in the laboratory. Review of antimicrobial results also
permits characterization of resistance mechanisms and the epidemiology of
resistant strains.
The software consists of three sections. 1) Data Entry. In addition to the
routine entry of susceptibility test results (disk diffusion, MIC, and/or
E-test), this program permits printing, retrieval, and correction of
clinical records as well as immediate feedback on test results. If data are
converted from an existing laboratory system, for example with BACLINK,
direct entry of data into WHONET is unnecessary. 2) Data Analysis.
Currently supported analyses include listings and summaries of isolates by
user-defined criteria; tabulation of the percentages of resistant,
intermediate, and susceptible isolates by species; zone diameter and MIC
histograms; scatterplots of zone diameter versus zone diameter or MIC
versus MIC; scatterplots of zone diameter versus MIC scatterplots and the
calculation of zone diameter/MIC regression curves; listings and summaries
of isolates by resistance profile; and automated screening of the data for
unusual isolates. 3) Configuration Program. This program permits the user
to enter and modify laboratory-specific information such as patient-care
areas, antibiotics and interpretive breakpoints, language, and hardware.
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Getting the Handle off the Proverbial Pump: Communication Works
Lela F. Folkers,* Maria Teresa Cerqueira,† Robert E. Quick,* James Kanu,*
and Gauden Galea‡
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †Pan
American Health Organization, Washington, D.C., USA; and ‡University of
Malta, Zebbug, Malta
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Health Promotion, Communication, Education, and Community Participation: A
Theory-Based Framework
During the last decades of this century, we have come to recognize that
human and social development are affected by the health status of the
population and that medical care alone cannot fully address all the
determinants of health. Health promotion strengthens primary health care
and contributes to public health by enabling people to become involved in
community action for health while working to maintain healthy lifestyles
and behavior. Health promotion is part of the communications effort
involved in the prevention and control of emerging infections.
Health promotion, as defined by various international and regional health
promotion conferences (Ottawa 1986, Adelaide 1988, Sundsvall 1991, Bogota
1992, Port of Spain 1993, and Jakarta 1997), enhances intersectoral action
by increasing the focus on community involvement and action for health,
placing healthy public policy on the agenda, creating supportive
environments, and developing personal health skills. Health promotion is
one of five policy directives of the Pan American Health Organization
(PAHO) Strategic and Programmatic Orientations for 1995-1998. The
PAHO/World Health Organization (WHO) Regional Plan of Action for Health
Promotion includes the following objectives: 1) promote social development
based on principles of equity and the right of citizens to health and
well-being; 2) strengthen the concept of a health culture based on healthy
environments, behavior, and lifestyles; and 3) develop the health sector's
capacity to recognize, support, and lead intersectoral processes for
promoting health.
To fully meet the goals of health promotion and disease prevention,
programs must inform and guide policies, plans, and activities for health.
Health education, communication, and community participation have a wide
range of theoretical frameworks. Among the more important are 1)
participatory community development political theories that explain
capacity building, democratic organization, and management styles; 2)
community-based social support networks that facilitate interpersonal
communication and consensus around healthy lifestyles; 3) learner-centered
cognitive theories that describe and explain the process of acquiring and
updating values, knowledge, and skills; and 4) the behavior change
framework, especially persuasion theories that describe and explain the
process of adoption of healthy lifestyles, both individually and
collectively. These theories create supportive environments, strengthen
community action, develop personal health skills, and sustain positive
behavior change.
Diarrhea Prevention through Point-of-Use Disinfection and Safe Storage of
Water: The Need for Innovative Interventions to Change Behavior
In many parts of the developing world, drinking water is collected from
unsafe sources and is further contaminated during storage in household
vessels. Simple, inexpensive disinfectant generators, better storage vessel
designs, and community education allow families to disinfect drinking water
immediately after collection and to store treated water in narrow-mouth,
lidded vessels designed to prevent recontamination. This three-component
prevention strategy has been field tested in Bolivia and Guatemala with
remarkable success. Urban and rural families readily accepted the vessels
and disinfectant, operated disinfectant generators, reliably obtained
adequate levels of free chlorine in stored water, and produced from
contaminated sources potable water that met WHO standards for microbiologic
quality. One study showed that the intervention reduced diarrheal disease
episodes in children and infants by 44%. Guatemalan street vendors added a
soap dish beside the water vessel to produce safer drinks and attract more
customers. In Bolivia, water vessels and disinfectant are now commercially
produced and marketed. Although the intervention costs less than US$1.00
per person per year and water vessels have been well accepted, in several
projects the use of chlorine disinfectant has decreased over time. Health
communication and initial adoption of water vessels alone has not changed
the long-term water treatment behavior in a large percentage of the
population. Formative research is needed prior to implementing these
projects, and innovative behavioral techniques are needed to motivate and
sustain behavioral change.
Lassa Fever Prevention In Endemic and Epidemic Situations—Sierra Leone
Lassa fever, a viral disease prevalent in West Africa, was first described
in a village called Lassa in northern Nigeria. The disease affects healthy
persons of all ages and both sexes and results in severe acute illness with
a 16% death rate. The virus is transmitted from rodents to humans and from
person to person. The disease is a major cause of illness and death in
disease-endemic areas in Sierra Leone.
In 1976, the Lassa Fever Research Project was established as a
collaborative effort between the Centers for Disease Control and Prevention
and the Ministry of Health in Sierra Leone. The mandate was to study all
aspects of the disease including epidemiology, diagnosis, treatment,
prevention, and control. In the intervening years much has been learned
about the virus and the disease it causes. Ribavirin, a drug effective
against the disease, is not easily accessible, and no vaccine is available;
therefore, prevention of endemic Lassa fever is vital. A multidisciplinary
strategy for prevention and control has been developed and includes three
components: clinical therapy, public education, and rodent control.
Physicians at regional hospitals and village health workers have been
trained to recognize the disease and its symptoms and to isolate and treat
Lassa fever patients. Public education and communication activities have
helped the general population recognize the disease and prevent
transmission. Additional education and training provided information on how
to reduce contact between humans and rodents. These promising approaches
were disrupted by civil war.
A January 1996 outbreak lasted until April 1997. Of 664 reported cases, 427
were confirmed Lassa fever cases; 82 patients died. In response to the
outbreak, an isolation and referral network was established and an
emergency training workshop on surveillance, case management, prevention,
and control of Lassa fever was organized for 40 health-care workers in two
districts in Eastern Province. Lassa fever continues to be a major health
problem in Eastern Province of Sierra Leone.
Healthy Islands and Emerging Infectious Diseases
In March 1995 in Yanuca Island, Fiji, the Western Pacific Regional Office
of WHO introduced the Healthy Islands program. This program recognizes the
peculiar character of island settings and seeks to reorient health and
developmental planning in a manner that addresses this character. This
approach to health promotion, which takes into account the setting of a
particular health problem, has become prevalent since the Ottawa Health
Promotion Conference in 1986.
Island states have contributed to the epidemiologic study of infectious
diseases in areas such as the delineation of area-species or
population-disease relationships and the history of infectious disease.
This contribution stands to repeat itself as many modern island nations
exhibit the factors that have been linked to the emergence of infectious
disease, including economic vulnerability; unsustainable resource use;
substantial internal migration; breakdown of water, sanitation, and public
health services (especially in areas of rapid urbanization); and large
inflows of tourists. Healthy Islands projects aimed at holistic solutions
to these problems have addressed, for example, malaria control in the
Solomon Islands, environmental health protection in Fiji, and water supply
and sanitation in Tonga. These projects have included health communication
with community development approaches directed at the peculiar problems of
the island setting.
The Internet helps promote some of the principles of the Healthy Islands
approach. The Internet promises to be an excellent tool for overcoming
professional isolation, a major shortcoming of the island setting, and
providing authoritative and timely access to information. Two projects
demonstrate this approach: The SYNAPSE is a network of health-care
professionals in the Mediterranean island of Malta, and Pacnet is an
electronic mailing list run by the Secretariat of the Pacific Community as
a forum for public health practitioners with an interest in the Pacific.
The Internet also serves to illustrate the "small-scale syndrome." The
logistic problems that render small economies vulnerable increase the cost
of bandwidth per head of population in small isolated communities. The
skills to effectively use the technology are scarce and the cost of
introduction great. Solutions like the Internet, appropriate in larger
countries, are relatively costlier and may be less appropriate in smaller
contexts.
The Internet is a good metaphor for Healthy Islands programs that seek to
apply technology imported from larger countries and adopt it within
cost-effective, holistic frameworks for health promotion. These solutions
are relevant to the small isolated context, address issues that cut across
sectoral and health service boundaries, and tend to be potentiated by
concerted regional action.
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Communicating Infectious Disease Information to the Public
Elias Abrutyn
Allegheny University of the Health Sciences, Philadelphia, Pennsylvania,
USA
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At one time, information about the science of medicine was almost the sole
purview of physicians and scientists, and the vehicle of communication was
predominantly the scientific journal. Today, a broad audience is interested
in the results of scientific investigations, which are disseminated widely
in a variety of media. This session sought to provoke discussion about
scientific communication in the broadest sense and to describe the roles
and perspectives of science writers and journalists.
Robin Cook, a science fiction writer, described two experiences during his
medical training that prompted him to become an author: He realized that
medicine involved high drama with star quality, and he noted a tremendous
gulf between what physicians knew and what the public knew about medicine.
Physicians and scientists need to recognize basic differences between the
goals of medical professionals and the goals of the media. Physicians and
scientists seek to transmit information; the media, on the other hand, seek
to entertain in addition to transmitting information. Fiction is a powerful
tool because it places information in an emotional context that people
remember, and its message has lasting influence.
Nichols Fox, a free-lance writer, discussed her interest in foodborne
infectious diseases, particularly Escherichia coli diarrheal disease.
Sometimes, in their research, reporters arrive at conclusions that are not
entirely objective. The following are some of the conclusions Nichols Fox
shared with the panel. 1) When you close the door on one microbe, you open
the door for another. 2) Measures that make food more affordable may also
increase disease risk. 3) Efficiency may not be the most important issue in
food production, and in a cost-benefit analysis, the people benefitting are
not always the ones sharing the cost. 4) Treatment of food animals and risk
for disease are related. 5) Recycling food animals, particularly diseased
animals, into animal feed can cause problems.
Laurie Garrett, science and medical writer for Newsday magazine,
highlighted the ability to place events within a historical perspective,
discussed reasons for differing viewpoints of the same events (particularly
differences between journalists and scientists), and suggested ways in
which journalists and scientists can broaden public perspective.
Paraphrasing Barbara Rosenberg of the Harvard School of Public Health,
Laurie Garrett noted public health professionals cannot see their work in a
historical light. At the same time, seeing events in such light may not be
possible. Further, each person's perspective is determined by cultural,
educational, and other factors; therefore, alternative views of the same
event should be allowed.
Like public health professionals, journalists need to consider the
historical perspective as they deal with the task of reporting daily
events. Journalists and scientists should gauge the current and future
import of an event and examine how it reflects on events of the past. The
Heisenberg principle of uncertainty also applies to epidemiology. When you
see an event, you alter it—in particular, you bring your cultural
perspective to it. Cultural perspective and scientific training affect
interpretation of events and should be taken into account when making
observations.
Journalists and authors of science fiction may make the scientific
community uncomfortable with probing questions. Sometimes they simply
reflect a different point of view or perspective; sometimes they make
historical connections not plainly obvious to everyone. With a broad view
in mind, scientists and journalists can bring a larger perspective to the
public.
Patricia Cornwell, a crime novelist, noted that two sayings are wellknown
in the morgue: the case is only as good as the evidence (a book is only as
good as the existing research), and, as forensic pathologists say, people
often die in the way that they lived–a saying not true about infectious
diseases and bioterrorism in which the randomness is striking.
The session's message was that scientists should view science writers as
the scribes who can disseminate a story to the public by translating
technical language into accessible terms. Scientists, like science writers,
should cultivate good sources and pick stewards who will communicate the
information accurately. The world wants to know about emerging threats to
health, and writers can help.
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APEC Emerging Infections Network: Prospects for Comprehensive Information
Sharing on Emerging Infections within the Asia Pacific Economic Cooperation
Ann Marie Kimball,* Carrie Horwitch,* Patrick O'Carroll,† Sumarjati
Arjoso,‡ Chaiyos Kunanusont,§ Ya-Shin Lin,* Clifford Meyer,* Laura
Schubert,* and Phillip Dunham*
*University of Washington, Seattle, Washington, USA; †The Centers for
Disease Control and Prevention, Atlanta, Georgia, USA; ‡Ministry of Health,
Indonesia; and §Ministry of Public Health, Thailand
------------------------------------------------------------------------
Trading blocs realize the strategic importance of and threats from emerging
infections, particularly those related to travel and food. Like the
European Union, the Asia Pacific Economic Cooperation (APEC) is undertaking
an initiative in emerging infections.
The APEC Emerging Infections Network project builds on an existing
Internet-based educational network (APEC EduNet), created to help link APEC
"study centers" at designated universities. Use of collaborative tools,
such as e-mail and the World Wide Web, helps bridge the broad geographic
expanse and diversity of APEC economies, permitting scientists and policy
makers to share information and more effectively combat emerging infectious
disease through surveillance, prevention, research, and control measures.
In the project's first year, staff made site visits to Thailand, Indonesia,
the Philippines, and Canada, and compiled information regarding Internet
access in these selected economies. Multidrug-resistant tuberculosis
(MDRTB) was selected as a disease priority by the partner economies.
Accurate, prospective surveillance data on MDRTB are not generally
available. Information sharing by e-mail and automated e-mail lists has
been successful, and feedback suggests these strategies will become
increasingly useful. The Emerging Infections Network (EINet) Web site
includes project information, surveillance data, policy discussion,
prevention guidelines, and distance learning resources about emerging
infections.
Human networking is as important as technology-based networking in
addressing emerging infections. Technology is adequate to support
communications if a comprehensive telecommunications strategy is used.
APEC, unlike the European Union, does not have the treaty basis to support
this intercountry collaboration, so memoranda of understanding are needed
to facilitate sustainable surveillance information flow and scientific
cooperation. Numerous member economies are eager to be included in project
activities. In the second year the project is expanding both in terms of
breadth of information and geography of economies.
Additional Information
1. Kimball AM. Pacific Rim economic ties spur emerging infections
network. Washington Public Health 1997;22.
2. Lance CR, Joseph CA, Bartlett CLR. European surveillance of
travel-associated Legionnaires disease. Slide presentation at the
International Conference on Emerging Infectious Diseases, Atlanta.
3. WHO/IUATLD. Global project on anti-tuberculosis drug resistance
surveillance, 1994-1997. Geneva: World Health Organization;1997. p.
1-227.
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Controversies in the Prevention and Control of Antimicrobial Drug
Resistance
David Bell
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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In Hospitals
William Jarvis, Centers for Disease Control and Prevention (CDC), discussed
antimicrobial resistance related to hospitalization. Two major factors
contribute to the emergence and spread of antimicrobial resistance in
hospitals: a high rate of antimicrobial drug use and inadequate infection
control practices. Much antimicrobial drug use in hospitals is
inappropriate (e.g., the use of vancomycin to treat a staphylococcal
infection susceptible to methicillin, or the continuation of perioperative
prophylaxis beyond 24 to 48 hours). Educational efforts on antimicrobial
drug use in hospitals have had mixed success. More aggressive and
controversial approaches to improve the use of these drugs have been
proposed; for example, excluding certain drugs (such as vancomycin) from
the routine reporting of susceptibility results; monitoring antimicrobial
use with feedback to physicians concerning inappropriate use;
antibiotic-use audits targeting problem areas (e.g., no diagnostic test
done, more than four drugs used during one hospitalization, use for more
than 3 weeks continuously); regulating drug promotion; requiring
justifications for use; using computer-generated stop orders; and
developing formularies, restrictions, and protocols by a multidisciplinary
team.
In Communities
Keith Klugman, South African Institute of Medical Research, spoke on
community-acquired infections, focusing on respiratory pathogens. One
controversial area concerns the extent to which drug resistance identified
in the microbiology laboratory correlates with clinical failure. Since
clinical trial data are frequently unavailable, assessment of drug efficacy
is often based on pharmacodynamics; i.e., a drug is believed efficacious if
its concentration at the site of infection exceeds the organism's MIC.
Otitis media and meningitis studies support this approach. In Pakistan,
laboratory data indicate that 78% of pneumococci are resistant to
co-trimoxazole, yet the clinical treatment failure rate is only 15%. The
reasons for this discrepancy are unknown, but the issue is important
because alternative drugs are more expensive. Standardization of laboratory
methods and appropriate surveillance methods are essential.
Another controversial area involves antibiotic use and how to improve it.
For many infections, the optimal dose and duration of therapy are unknown.
Antibiotics are often prescribed inappropriately because physicians are
uncertain when antibiotics are indicated and patients demand them;
educating both of these groups is a challenge. Better diagnostics to reduce
empiric therapy would be helpful. Other areas of uncertainty include the
use of vaccines to decrease colonization and infection with resistant
organisms and the extent to which antibiotics given for a specific
indication might lead to resistance in different organisms.
In Veterinary Medicine
Klaus Stoehr, World Health Organization (WHO), addressed controversies
related to use of antibiotics (preventive, therapeutic, growth- promoting)
in food animals. Some antibiotic use contributes to the pool of resistant
human pathogens. Both medical and nonmedical uses of antibiotics should be
reduced. More scientific data are needed to address issues related to
antibiotic use in food animals, including elucidating the human health
impact, e.g., the percentage of resistance genes or resistant organisms
originating in animals and the extent to which therapy of zoonotic
bacterial infections in humans has been compromised because of resistance.
The economic benefits of subtherapeutic antimicrobial use for growth
promotion are also controversial; one study estimates that production costs
without such use would increase by up to 8%, but recent experience in
Sweden indicates that meat produced without growth promotants can be priced
competitively. A WHO meeting in 1997 on the medical impact of antibiotic
use in livestock production recommended antimicrobial resistance monitoring
and prudent use of antibiotics in food animals.
In Developing Countries
Antonio C. Pignatari, Escola Paulista da Medicina, São Paulo, Brazil,
discussed antibiotic resistance issues in developing countries. More than
two thirds of the world's population lives in developing countries, where
the contrast between wealth and poverty is extreme. Infectious diseases
represent the main public health problem. Because of inadequate resources
for surveillance, control, and treatment, antimicrobial-resistant
infections have become a major problem with serious implications for the
health system and the economy. The main problems with drug resistance are
seen in the treatment of diarrheal diseases, sexually transmitted diseases,
pneumococcal infections, tuberculosis, nosocomial infections, and malaria.
Restrictive antimicrobial use policies (which are controversial) can be
effective in the hospital but are difficult to implement in the community.
In many areas, the availability of medical care is limited; thus, laws
requiring a physician's prescription for antibiotics are difficult to
enforce. Pharmacies provide an important service in dispensing medications,
yet most developing country pharmacists have limited training. The use of
antimicrobial drugs in food animals is also a problem in developing
countries, and no controls are in place to address it. Control of
antimicrobial resistance and emerging infections in developing countries
cannot be achieved without addressing closely related social and economic
issues.
In Clinical Laboratories
Fred Tenover, CDC, addressed antibiotic resistance issues in the
microbiology laboratory. Laboratorians must move from susceptibility
testing to finding resistance. A common misconception is that new
resistance mechanisms are easily identified because they result in high
MICs and low zone sizes. However, many new resistance mechanisms lead to
MICs close to the breakpoint for resistance. More sensitive screening tests
are being introduced to detect resistance, but they cannot replace MICs;
therefore, laboratory workload is increasing in an era of downsizing.
Several "drug-bug" combinations are problematic and require new approaches.
For detecting nonsusceptibility (intermediate or full resistance) of
staphylococci to vancomycin, the traditional method of disk diffusion
testing is not reliable. Acceptable methods include the Brain Heart
Infusion vancomycin agar screening test developed for enterococci or broth
microdilution tests held 24 hours. For pneumococci, testing for
susceptibility to both penicillin and extended spectrum cephalosporins is
important because resistance to these drugs is becoming more common. For
invasive isolates where the need to detect resistance is urgent, the
oxacillin screening test should not be used; MIC methods should be used
directly. For gram-negative bacilli, traditional methods to detect
resistance to extended spectrum beta-lactam drugs are inadequate, although
the latest National Committee for Clinical Laboratory Standards guidelines
present effective screening tests. Finally, sensitivity must be determined
for clinically important isolates treated with fluoroquinolones, since
selective pressure for resistance is increasing as a result of widespread
use.
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Infectious Causes of Chronic Inflammatory Diseases and Cancer
Gail H. Cassell
Lilly Research Laboratories, Indianapolis, Indiana, USA
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Powerful diagnostic technology, plus the realization that
organisms of otherwise unimpressive virulence can produce
slowly progressive chronic disease with a wide spectrum of
clinical manifestations and disease outcomes, has resulted in
the discovery of new infectious agents and new concepts of
infectious diseases. The demonstration that final outcome of
infection is as much determined by the genetic background of
the patient as by the genetic makeup of the infecting agent is
indicating that a number of chronic diseases of unknown
etiology are caused by one or more infectious agents. One
well-known example is the discovery that stomach ulcers are due
to Helicobacter pylori. Mycoplasmas may cause chronic lung
disease in newborns and chronic asthma in adults, and Chlamydia
pneumoniae, a recently identified common cause of acute
respiratory infection, has been associated with
atherosclerosis. A number of infectious agents that cause or
contribute to neoplastic diseases in humans have been
documented in the past 6 years. The association and causal role
of infectious agents in chronic inflammatory diseases and
cancer have major implications for public health, treatment,
and prevention.
The belief that infectious agents are a cause of chronic inflammatory
diseases of unknown etiology and of cancer is not new. Approximately 100
years ago, doctors noted a connection between cervical cancer and sexual
promiscuity that transcended mere coincidence (1). By 1911, a connection
between viruses and cancers in animals had become well established (2). As
early as the 1930s, mycoplasmas were proposed as a cause of rheumatoid
arthritis in humans, and shortly thereafter, they were proven to be the
most common cause of naturally occurring chronic arthritis in animals (3).
Proof of causality of cancer and arthritis in humans was more difficult.
When searches for infectious agents in cancer and arthritis found none,
research began to focus on mechanisms of inflammation, tumorogenesis, and
drug discovery. More recently, however, scientists have renewed searches
for infectious agents.
Advances in molecular biology and medical devices have revolutionized our
ability to detect very low numbers of infectious agents in specimens
collected directly from the affected site. HIV has demonstrated the ability
of infectious agents to produce slowly progressive, chronic disease with a
wide spectrum of clinical manifestations and disease outcomes. Increased
understanding of the body's defense mechanisms and the demonstration that
final outcome of infection is as much determined by the genetic background
of the host as by the genetic makeup of the infecting agent suggest that a
number of chronic diseases of unknown etiology may be caused by an
infectious agent.
Recent data suggest a role for one or more infectious agents in the
following chronic diseases: chronic lung diseases (including asthma),
cardiovascular disease, and cancer. Many of the agents implicated are
commonly transmissible and are either treatable with existing antibiotics
or are potentially treatable with antiviral drugs. Thus, proof of causality
in any one of these diseases would have enormous implications for public
health, treatment, and prevention. Few areas of research hold greater
promise of contributing to our understanding of infectious diseases and the
eventual relief of human suffering.
The intent of this paper is not to provide a comprehensive review of
chronic inflammatory diseases of unknown etiology and the agents implicated
but rather to utilize several models to discuss available data and to
illustrate the difficulty in proving causality in chronic inflammatory
diseases. The discussion is based upon the following assumptions. Most
chronic inflammatory diseases are likely multifactorial. Heredity,
environment, and nutrition are critical determinants of disease expression
with heredity being the most important.
Theoretically, chronic inflammatory diseases currently of unknown etiology
could result from three different types of pathogens: 1) those that are
fastidious and previously recognized but because of their fastidiousness or
lack of appreciation of their disease-producing potential are not included
in the differential diagnosis, and 2) infectious agents previously not
recognized that therefore go undetected. Infection with either group can
result in misdiagnosis and lack of treatment. Depending upon the biology of
the organism and intrinsic and extrinsic factors of the host the organism
can persist, resulting in chronic inflammation. The third group of
pathogens would be those that elicit an autoimmune response resulting in
persistent inflammation without the persistence of the inciting agent.
Examples of the first two groups of pathogens will be discussed here using
mycoplasmas to typify the first group and Chlamydia pneumoniae the second.
Finally, recent advances in our understanding of the role of infectious
agents in cancer will also be summarized.
Chronic Lung Diseases
Murine Chronic Respiratory Disease as a Model System
The difficulty in establishing the infectious etiology of a chronic
obstructive lung disease is well illustrated by Mycoplasma pulmonis and
murine chronic respiratory disease. Proof that M. pulmonis can cause this
disease took nearly 50 years and required inoculation of germ-free animals
(4). Chronic bronchopneumonia in rats was first described in 1915 when this
species came into general use for experimental purposes (5). In
approximately 1940, a Mycoplasma, later identified as M. pulmonis, was
recognized as a possible cause (6), but the ubiquity of the organism and
its frequent isolation from healthy as well as diseased rats and mice (even
from trachea and lungs) soon gave it the reputation of being a commensal
with little pathogenic potential. The failure of pure cultures of this
organism to consistently produce disease of the lower respiratory tract
also precluded its acceptance as the etiologic agent. Only in the early
1970s was M. pulmonis alone shown to consistently reproduce all of the
characteristic clinical and pathologic features of the natural respiratory
disease when inoculated into animals maintained under germ-free conditions
(7). Subsequent studies provided explanations for previous difficulties in
reproducing the disease.
The respiratory disease caused by M. pulmonis is slow to begin and
long-lasting. Consequently, the disease has various stages of pathologic
lesions and a lack of uniform lesions, even among animals in the same cages
(due partly to variables that can affect development of the disease in the
lower respiratory tract, such as intracage ammonia produced by bacterial
action on soiled bedding, synergy with murine respiratory viruses and other
bacterial pathogens, and nutritional factors) (7). However, comparison of
animals matched for age, sex, and microbial and environmental factors
indicates that heredity is the most critical determinant of susceptibility,
lesion character, and disease severity. Susceptibility among animal species
and among strains of the same species differ dramatically (8-11).
Intranasal inoculation of M. pulmonis produces markedly different lesions
in F344 rats and in CD-1 mice, even when the dose is comparable on the
basis of lung and body weight. In rats the lesions progress slowly from the
upper respiratory tract distally, with alveolar involvement occurring days
to months following inoculation, whereas in mice, alveolar lesions develop
within hours after infection and are responsible for acute alveolar disease
and death within 3 to 5 days. Depending on their genetic background, mice
that survive the acute disease develop chronic lung disease characterized
by bronchiectasis that persists for up to 18 to 24 months or the lifetime
of the animal.
Studies of naturally occurring and experimentally induced disease indicate
that M. pulmonis also causes a slowly progressing upper genital tract
disease in LEW and F344 rats (18). Pups can become infected in utero, at
the time of birth due to cervical and vaginal infection of the dams, or via
aerosol from dams shortly after birth. Even though the organisms can be
shown to colonize the ciliated epithelium of the upper and lower
respiratory tracts of pups, microscopic lesions are not detectable for 2 to
6 months depending on the strain of rat. Development of obstructive lung
disease can require as long as 12 to 18 months.
Differences in severity and progression of the lung lesions due to M.
pulmonis in LEW and F344 rats are related to differences in the degree of
nonspecific lymphocyte activation in the two strains or an imbalance in
regulation of lymphocyte proliferation in LEW rats (12). M. pulmonis
possesses a potent B cell mitogen, and, in addition, the organism is
chemotactic for B cells (13). Interestingly, LEW rats are also more
susceptible to other chronic inflammatory diseases, including streptococcal
cell-wall induced arthritis, adjuvant-induced arthritis, and allergic
encephalomyelitis (12).
Ureaplasma urealyticum as a Cause of Pneumonia in Newborns and Its
Association with Chronic Lung Disease (CLD) in Premature Infants
Respiratory dysfunction represents the most common life-threatening problem
in premature infants and one of the largest costs of neonatal intensive
care (14). Infants weighing less than 1,000 g at birth are more likely than
those with greater birth weights to die within the first few days of birth
of respiratory-related problems; those who survive are at an increased risk
of CLD (15). Approximately 20% of stillborn babies and infants dying within
72 hours of delivery have histologic evidence of pneumonia (16). Yet the
true incidence of lower respiratory infection acquired either in utero or
at the time of delivery and its contribution to death or development of CLD
are unknown. The cause of lower respiratory disease in newborn babies is a
diagnostic dilemma because pneumonia in early neonatal life is usually
clinically and radiologically indistinguishable from surfactant-deficiency
syndrome (17). Furthermore, meaningful cultures from the lung are not
easily obtained, whereas cultures of the throat, nasopharynx, and blood are
unrevealing or misleading.
Pneumonia
The mycoplasma U. urealyticum, a common commensal of the lower female
genital tract, has recently been shown to cause respiratory disease in
newborn infants. Retrospective (18) and prospective (19-21) studies
indicate an association of U. urealyticum with congenital pneumonia. Case
reports also provide evidence that U. urealyticum is a cause of pneumonia
in newborn infants (22-23). The organism has been isolated from affected
lungs in the absence of chlamydiae, viruses, fungi, and bacteria and in the
presence of chorioamnionitis and funisitis (40) and has been demonstrated
within fetal membranes by immunofluorescence (24) and in lung lesions of
newborns by electron and immunofluorescent microscopy (20). The specific
immunoglobulin (Ig) M response in several cases of pneumonia in newborns
further documents in utero infection (20).
We have found that U. urealyticum is the single most common microorganism
isolated from endotracheal aspirates of infants who weigh =2,500 g and who
require supplemental oxygen within the first 24 hours after birth (19).
Infants weighing =1,000 g and from whom U. urealyticum is isolated from the
endotracheal aspirate are twice as likely to die as infants of similar
birth weight but who are uninfected or infected infants >/1,000 g. These
findings support the hypothesis that only a select group of infants, i.e.,
those with very low birth weights, is subject to disease due to U.
urealyticum. This fact may account for the seeming disparities in
conclusions regarding the role of U. urealyticum in neonatal respiratory
disease reached in earlier prospective studies that failed to distinguish
this subpopulation at high risk from the whole (25,26).
That endotracheal isolations of U. urealyticum represent true infection of
the lower respiratory tract is supported by initial isolation of
ureaplasmas in numbers exceeding 1,000 CFUs (and sometimes exceeding 10,000
CFUs) and repeated isolations of the organism from tracheal aspirates for
weeks and even months in some infants that continue to require mechanical
ventilation. That the tracheal isolates are not merely a reflection of
contamination from the nasopharynx is supported by the discrepancy in
isolation rates between the two sites and recovery of U. urealyticum in
pure culture from endotracheal aspirates in more than 85% of the infants
(19). Concomitant recovery of the organism from blood of up to 26% of those
with positive endotracheal aspirates and from cerebrospinal fluid (CSF) of
some infants indicate that in some infants the organism is invasive (19).
Fourteen percent of U. urealyticum endotracheal isolates were from infants
born by cesarean section with intact membranes, indicating that in utero
transmission occurs rather commonly, at least in premature infants.
In a study of 98 infants, respiratory distress syndrome, the need for
assisted ventilation, severe respiratory insufficiency, and death were
significantly more common among those infants <34 weeks gestation from whom
U. urealyticum was recovered from endotracheal aspirates at the time of
delivery than among uninfected infants (27). U. urealyticum was isolated
from 34% of blood cultures and also from four of six CSF samples and in 6
of 11 postmortem brain and lung biopsy pecimens. Eighty-two percent of the
ureaplasma isolates were present in pure culture, and 48% of infants born
by cesarean section with intact membranes had ureaplasmas isolated from one
or more sites.
U. urealyticum can induce ciliostasis and mucosal lesions in human fetal
tracheal organ cultures (20). Furthermore, we have shown that ureaplasmas
isolated from the lungs of human infants with congenital and neonatal
pneumonia produce a histologically similar pneumonia in newborn mice (28).
Even in this mouse model, age is a critical determinant of disease. Newborn
mice are susceptible to colonization of the respiratory tract and
development of pneumonia; 14-day-old mice are resistant.
We have shown that endotracheal inoculation of premature baboons
(well-established models of premature human infants) with U. urealyticum
isolated from human infants results in the development of pathologically
recognizable pulmonary lesions, including acute bronchiolitis with
epithelial ulceration and polymorphonuclear infiltration, which is
distinguishable from hyaline membrane disease (29). U. urealyticum can be
isolated from blood, endotracheal aspirates, and pleural fluid and lung
tissue from some of these animals 6 days after infection.
The available evidence provides a strong argument that U. urealyticum is a
common cause of pneumonia in newborn infants, particularly those born
before 34 weeks of gestation. The organism can be isolated from
endotracheal aspirates in up to 34% of infants weighing <2,500 g;
radiographic evidence of pneumonia is twice as common in these infants as
in U. urealyticum negative infants (30% vs. 16%, p = .03) (30). Many of
these infections develop as a result of in utero exposure. Cases of
ureaplasmal pneumonia occur much less frequently in term infants. These
findings in infants are consistent with the fact that U. urealyticum
infection of the chorioamnion is also much more common before 34 weeks of
gestation. Lack of transplacental passage of immunoglobulin prior to 32
weeks gestation (31) may partially explain these findings. Experience from
mycoplasmal respiratory diseases of animals indicates that preexisting
antibody is protective, whereas antibody in the presence of an established
infection is rarely effective in elimination of the organism (32).
CLD in Premature Infants
Some, but not all, studies (33-36) show an association between isolation of
U. urealyticum from the respiratory tract of newborn infants and the
development of CLD (33). Differing results may be obtained because some
studies do not limit culture isolation to the affected site (the lower
respiratory tract), do not limit their patient population to those at
greatest risk (birth weight <1,000 g); or do not limit culture isolation to
within 12 hours of delivery, i.e., most likely infected in utero. Several
facts suggest that infants who acquire U. urealyticum in utero may be at
greatest risk for development of CLD. Dyke et al. (34) found U. urealyticum
in the gastric aspirates of infants =1,000 g was associated with a
significantly increased risk of CLD in those infants delivered by cesarean
section but not in those delivered vaginally. This could result from a
longer exposure to U. urealyticum as a result of in utero exposure, or it
may be a reflection of differences in the virulence of those organisms
found only in the cervix versus those that have invasive potential and that
can cause an ascending infection from the vagina into the uterus. Along
these lines it is of interest that a recent study of 49 preterm infants
which included only three infants from whom U. urealyticum was recovered
within 24 hours of birth found no association with development of CLD (35).
The remaining 11 infants were not culturally positive until 48 to 72 hours
after birth suggesting that only the three study infants were infected in
utero. In another recent study reported by Valencia et al. (36) CLD was
found in 26% of U. urealyticum infected infants compared to only 4.7% of
the noncolonized group. However, these results were not statistically
significant possibly because of the small number of patients studied but
also possibly because 22% of the patients included did not have cultures
performed until between 2 days and 3 months postnatal life.
Isolation of U. urealyticum from endotracheal aspirates is not only a risk
factor for development of pneumonia but also of precocious dysplastic
changes (30). Walsh et al. (38) isolated U. urealyticum directly from
pleural fluid and tissue collected by open lung biopsy in four of eight
infants cultured who had CLD. We (19) continued to recover ureaplasmas from
endotracheal aspirates of infants with CLD for months following initial
recovery of the organism from endotracheal aspirates within 12 hours of
birth.
Available evidence creates a cohesive argument that U. urealyticum
infection of the lower respiratory tract is a likely risk factor for, and
not only associated with, CLD. Because U. urealyticum has only recently
been suggested as a cause of pneumonia in newborns, it is not routinely
sought by most hospital laboratories. Furthermore, the organism is not
susceptible to antibiotics used prophylactically in very low birth-weight
infants with evidence of respiratory distress. Consequently, the infection,
i.e., pneumonia, goes undetected and untreated. Due to the difficulties in
diagnosis, most hospital laboratories do not culture for this organism.
The pathophysiology of CLD in premature infants suggests that U.
urealyticum produces undetected and untreated pneumonia and results in an
increased requirement for oxygen and subsequent development of CLD as a
result of oxygen toxicity (33,37) or a synergistic effect between the
ureaplasmas and hyperoxia. It has been proposed that hyperoxia-induced lung
injury contributes to development of CLD by stimulating the proinflammatory
cytokine interleukin (IL)-6 (38). U. urealyticum may also contribute to the
development of CLD by stimulation of proinflammatory cytokines. Infants
from whom ureaplasmas are isolated from endotracheal aspirates within the
first 24 hours of life are more likely to have neutrophils in their
tracheal aspirates on day 2 than are those not colonized (39). Aspirates
from colonized infants are also more likely to have class II cytology than
those from uncolonized patients at day 2 of life. This may explain why
ureaplasma-infected infants respond to dexamethasone therapy (39). These in
vivo findings are consistent with the recent demonstration of U.
urealyticum induction of IL-6 and IL-8 in human neonatal pulmonary
fibroblasts even in the absence of hyperoxia (38). Interestingly, together
ureaplasmas and hyperoxia resulted in greater stimulation of IL-6 and IL-8
than either alone. This is consistent with the synergism previously
demonstrated in vivo between ureaplasmal infection and hyperoxia (37).
Studies in mice also suggest that increased oxygen requirements of very low
birth-weight infants might predispose them to lower respiratory tract
infection or, alternatively, that U. urealyticum infection potentiates
oxygen-induced injury (28,37). Exposure to oxidants is known to enhance
respiratory disease and death due to M. pulmonis respiratory disease in
mice (41).
That U. urealyticum is a cause of pneumonia in newborns can no longer be
questioned. Data provide strong evidence that U. urealyticum can be a
primary cause or a contributing cofactor in development of CLD in humans,
but the data are not definitive. Cohort studies allow follow-up of exposed
persons and thus reduce bias, but the designs of these studies cannot rule
out the possibility that a third factor associated with U. urealyticum is
actually the true cause of CLD. However, a randomized trial of exposure to
infection in humans is not ethical or practical. Although a randomized
trial of antibiotic treatment could provide critical information related to
patient management, it would still not bring us closer to proving
causality. Even if treatment is found to be efficacious, conclusions about
causation will be limited by the fact that the third factor might also be
susceptible to the antibiotic chosen. If it is not found to be efficacious,
it may be because ureaplasma infection in utero or soon after birth results
in irreversible lung damage. Nevertheless, a treatment trial is urgently
needed to determine whether appropriate therapy can reduce the incidence of
illness and death associated with CLD. First, studies are needed to
determine dose and duration of antibiotic therapy and whether currently
available antibiotics will even eliminate the organism.
Mycoplasma pneumoniae and C. pneumoniae as Causes of Chronic Asthma
Asthma, a CLD characterized by airway obstruction, inflammation, and
bronchial hyperresponsiveness to a variety of stimuli, including
infections, is a common illness in both pediatric and adult populations. In
the United States alone, approximately 12 million people have asthma,
resulting in health-care costs of approximately 4.6 billion dollars
annually (42). In children, asthma is the most common reason for hospital
admissions and school absenteeism (43). Yet the etiology and pathogenesis
of this important disease remains poorly defined. Historically, viruses
that commonly infect the respiratory tract have been thought to play a role
in both provoking asthma exacerbations and in altering responses to other
environmental agents that might be involved (44).
M. pneumoniae is a common cause of both upper and lower respiratory
infection in humans; tracheobronchitis is the most common clinical
manifestation (45). Previously thought to cause acute, self-limited disease
primarily in persons between 6 and 21 years of age (45), M. pneumoniae is
now known to be the cause of pneumonia in 20% to 25% of all age groups and
to persist in certain persons for weeks to months, resulting in prolonged
reduced pulmonary clearance and airway hyperresponsiveness (46-47).
Epidemiologic evidence links mycoplasma infection with asthma exacerbation
and possibly with the pathogenesis of asthma (47-50).
While M. pneumoniae has been associated with exacerbations of asthma, its
role in sustaining chronic asthma or in initiating exacerbation is unknown.
However, the proven role of mycoplasmas in similar chronic respiratory
diseases of numerous animal species, including M. pulmonis in rodents,
suggests that careful, systematic studies should be undertaken in humans
(45).
C. pneumoniae, the most recently described Chlamydia species, has been
associated with a wide range of respiratory tract illnesses, from
pharyngitis to pneumonia with empyema (51). C. pneumoniae has been isolated
from 15% to 20% of adults and children with community-acquired pneumonia
(51). On the basis of serologic results only, C. pneumoniae has been
associated with acute exacerbations of asthma in adults (52); on the basis
of nasopharyngeal cultures, it has been associated with asthma in children
(53). In both children and adults, the organism persists for months in the
upper respiratory tract of patients with wheezing (54).
If M. pneumoniae, or for that matter any infectious agent, is a causal
factor in initiating and sustaining asthma in certain persons, the agent
should be present and persistent in the lungs of some persons with stable,
chronic asthma. We have recently undertaken a study to determine if M.
pneumoniae can be detected in the lungs of adults with stable, chronic
asthma versus asymptomatic controls (55). To facilitate interpretation of
results, we also evaluated the presence of other fastidious infectious
agents that have previously been implicated in the pathogenesis of asthma,
including the seven common respiratory viruses (44) and C. pneumoniae
(56,57).
M. pneumoniae was detected by PCR in 10 of 18 asthma patients and 1 of 11
controls (p = 0.02). All patients were culture, EIA, and serologically
negative for M. pneumoniae. All PCR and cultures were negative for C.
pneumoniae and all EIAs for respiratory viruses were negative. Nine persons
with asthma and one control exhibited positive serology for C. pneumoniae
(p = 0.05). For C. pneumoniae, the lack of correlation between serologic
results and culture and PCR was not unexpected. We have seen discordance
between culture and serologic results in patients with community-acquired
pneumonia (58,59), but in these cases more patients were culture positive
than seropositive. Thus, the culture methods we used in the study have
previously been shown to be valid.
Our failure to culture M. pneumoniae might be explained by its extreme
fastidiousness or its low numbers. Culture is the least sensitive of the
methods used in this study for detection of M. pneumoniae. However, the
culture methods we used in this study we also used to evaluate more than
2,000 respiratory specimens during the same period in patients with
radiographically confirmed, community-acquired pneumonia. These methods
have resulted in recovery of M. pneumoniae by culture in up to 17% of
patients (G. Cassell, et al., unpub. obs.; 58,59).
Recent studies indicate that some other mycoplasma species of human origin
may be able to survive intracellularly in chronic infections of cell
cultures (60). Likewise, some strains of M. hyorhinis, the etiologic agent
of chronic respiratory disease of swine, can become so adapted to growth in
the presence of cells that it is no longer cultivable on artificial media
(61). If this occurs in vivo, organisms like M. pneumoniae could be
difficult if not impossible to recover by culture.
In the absence of other known respiratory pathogens in other patient
populations, the presence of M. pneumoniae can be detected longer by PCR
than by either culture or serologic test. Guinea pigs experimentally
infected with M. pneumoniae become chronically infected as detected by PCR
for up to 200 days but are culture negative by 70 days. Also by 70 days,
antibody levels become negative (62). Thus, patients with asthma appear
chronically infected with M. pneumoniae, despite negative culture results,
because they are PCR positive. That positive PCR results truly reflect
involvement of the lower respiratory tract by M. pneumoniae is supported by
the fact that 9 of the 10 M. pneumoniae-positive patients were positive in
the bronchoalveolar lavage (BAL), bronchial biopsies, or bronchial brush
specimens. Furthermore, the organism was detected in the nasopharynx or the
throat of only five of the nine asthma-positive patients, thus indicating
that detection in the lower tract was not merely due to contamination by
organisms from the upper tract during sample collection. More importantly,
a significant number of persons with asthma were positive in the lower
respiratory tract on repeat sampling (2 to 4 months between samples), thus
indicating persistent colonization. By cloning and sequencing the PCR
product in BAL from several representative patients, we demonstrated 100%
sequence homology with M. pneumoniae. Use of multiple primer pairs as well
as confirmation of PCR findings in two different laboratories also attests
to the validity of the PCR results. Our failure to detect M. pneumoniae in
specimens from age-matched control patients as well as in specimens from
100 asymptomatic children using the same PCR methods further verifies the
specificity of our PCR methods and argues that finding M. pneumoniae in
persons with chronic asthma does not merely reflect a carrier state.
We have previously noted the lack of antibody response to M. pneumoniae in
both pediatric and adult populations with community-acquired pneumonia (G.
Cassell et al, unpub. obs.; 58,59,63). Study results indicate that a subset
of infected persons do not mount an antibody response, perhaps due to
genetic differences. Lack of antibody may in fact contribute to the
organism's persistence. The immunomodulatory properties of M. pneumoniae
(12) also could facilitate the organism's persistence.
Recent studies indicate that M. pneumoniae respiratory disease is often
misdiagnosed and inappropriately treated, which would also contribute to
persistence. Admitting physicians chose other pathogens as the most likely
agents in 46% of the cases subsequently documented as M. pneumoniae
infections (64). Even upon correct diagnosis, at least 10% of the patients
did not receive appropriate antibiotics during their hospitalization.
In summary, we have demonstrated that persons with chronic asthma, but not
healthy persons, exhibit evidence of M. pneumoniae colonization of the
lower airways. Like several other investigators (56,57), we found more
persons with asthma than control subjects had serologic evidence of C.
pneumonia infection. Further study is needed to determine if these findings
are an epiphenomenon or, as we expect, a pathogenic mechanism in asthma. If
the latter is correct, greater evaluation of the process involved is needed
to further our understanding of the pathogenesis and treatment of asthma.
Role of C. pneumoniae in Atherosclerosis
Infection was proposed as a cause of atherosclerosis by Sir William Osler
and others at the beginning of the century (65). However, it was not until
the 1970s that experimental infection of germ-free chickens with an avian
herpesvirus was found to produce arterial disease that resembled human
atherosclerosis (66). Associations have since been reported of human
coronary heart disease with certain gram-negative bacteria (i.e.,
Helicobacter pylori and C. pneumoniae) (67,68), with certain herpesviruses
(especially cytomegalovirus) (69), and with clinical markers of chronic
dental infection (70). Rather than an exhaustive evaluation of each of
these purported associations, it seems reasonable to focus on the
respiratory pathogen, C. pneumoniae, for which the evidence seems
strongest.
C. pneumoniae, like M. pneumoniae, is a common cause of community-acquired
pneumonia (70,71). C. pneumoniae infects more than 50% of people at some
point in their lives (51,71). It can often go undiagnosed and improperly
treated because again it is fastidious and diagnostic methods are not
routinely available. Even in the best reference laboratories, diagnosis can
be a challenge (71). It, like M. pneumoniae, is also thought to play a role
in acute asthma and chronic bronchitis (52) as well as to cause
extrapulmonary manifestations (51,71). It, like M. pneumoniae, can also
result in persistent infection following acute respiratory disease (54).
Eighteen seroepidemiologic studies evaluated the association of C.
pneumoniae infection and cardiovascular disease (67). Most found at least
twofold or larger odds ratios; some reported increasing odds ratios with
increasing antibody titers. The general consistency of their findings in a
total of 2,700 cases supports the existence of some real association
between C. pneumoniae and coronary heart disease because the studies were
done in different populations, used different criteria for cases, adjusted
for potential confounders to differing degrees, and were, therefore, prone
to different biases. While diagnosis by serology has its limitations, C.
pneumoniae has been demonstrated by a variety of laboratory techniques
(including culture, PCR, electron microscopy, and immunocytochemistry) in
the atherosclerotic lesions of coronary arteries, carotid arteries, aorta,
smaller cerebral vessels, and larger peripheral arteries (72-78). In the
more than 13 published studies of C. pneumoniae in human pathology samples
(67), chlamydiae were present in 257 (52%) of 495 atheromatous lesions but
in only 6 (5%) of 118 control samples of arterial tissue, yielding a
weighted odds ratio of about 10 (95% confidence interval 5-22). It seems
unlikely that sampling biases can entirely account for this extreme
difference between case and control tissue.
C. pneumoniae, an obligatory intracellular bacterium capable of causing
persistent infection and multiplying in endothelial and smooth muscle cells
and macrophages (79), can also be disseminated by macrophages (80). Hence,
some have argued that macrophages may ingest C. pneumoniae in the lung or
elsewhere before migrating to atheromatous lesions, in which case it may
only be a bystander. However, in two different rabbit models,
atherosclerotic changes develop only after infection with C. pneumoniae
(81,82). The organism by itself induces the production of cytokines (83)
and adhesion molecules (84), and it possesses an endotoxin (85) capable of
modulating the host inflammatory response. Thus, the biologic properties of
C. pneumoniae make it a logical candidate for triggering the chronic
inflammation found in atherosclerosis (82).
Finally, some studies have found rising or elevated levels of antibodies to
C. pneumoniae in some males during the months just preceding a heart attack
(86). Recent studies indicate that antibiotics given during or after a
first heart attack may decrease the risk of a second cardiac problem
(86-88). This finding also raises the possibility that antibiotics may have
a role in the treatment of cardiovascular illnesses; that could be
especially beneficial in developing countries where traditional treatments
like angioplasty are expensive.
Some have proposed additional large-scale antibiotic treatment trials in an
attempt to further prove causality. Several major issues need to be
resolved first. Ideally, one should treat patients with documented C.
pneumoniae infection; however, reliable diagnostic methods and treatment
protocols are lacking (71). Because most available antibiotics are
bacteriostatic, not bacteriocidal, some patients may remain infected up to
11 months after treatment. Even if these issues could be resolved,
antibiotic treatment trials will not prove causality, just as is the case
with U. urealyticum and CLD of prematurity or M. pneumoniae and chronic
asthma. The nonantimicrobial effects may also influence the outcome of such
studies. For example, tetracyclines can inhibit metalloproteinases, which
may contribute to acute coronary syndromes (89). Some macrolides have
antiinflammatory effects (90-93). Moreover, antibiotics are not selective,
thus making it impossible to determine the effects of treatment upon C.
pneumoniae versus other potential culprits, e.g., H. pylori, which is also
susceptible to tetracyclines and macrolides. However, if antibiotic
treatment could reduce atherosclerotic events, the public health
implications could be enormous.
Causal Role of Viruses and Bacteria in Cancer
Early in this century, Peyton Rous (2) established beyond doubt that cancer
can be caused by an infectious agent in chickens. Since then, evidence has
accumulated that other viruses cause cancer in a number of different animal
species (94). A growing body of research suggests that a number of viruses,
bacteria, and parasites cause cancer in humans, thus providing new
possibilities for treatment and prevention of cancer (94). In 1997, the
World Health Organization estimated that up to 84% of cases of some cancers
are attributable to viruses, bacteria, and parasites and that more than 1.5
million (15%) new cases each year could be avoided by preventing the
infectious disease associated with them (95).
H. pylori, found in the stomachs of a third of all adults in the United
States, causes inflammation of the mucous membrane of the stomach (96). In
20% of infected persons, H. pylori induces gastric ulcers (96). Peptic
ulcer disease, a chronic inflammatory condition of the stomach and
duodenum, affects as many as 10% of people in the United States at some
time in their lives. In the early 20th century, pathogenesis was believed
related to stress and dietary factors. Thus treatment focused on bed rest
and bland food. Later, gastric ulcers were believed to be caused by the
injurious effects of digestive secretions. Following the identification of
the histamine receptor that appeared to be the principal mediator of
gastric acid secretion, antagonists of this receptor were used for therapy
for peptic ulcer disease. In 1982, H. pylori was first isolated from the
human stomach, but it was not until one decade later and after Marshall
ingested pure cultures of the organism that causality was accepted by the
medical and scientific community (97).
In 1994, the International Agency for Research on Cancer concluded that
infection of humans with H. pylori is causally associated with the risk of
developing adenocarcinoma of the stomach (98), one of the most common
malignancies in the world, although relatively uncommon in the United
States (24,000 new cases and 14,000 deaths per year). However, also in
1994, a Consensus Panel of the National Institutes of Health (NIH)
concluded that available evidence was insufficient to recommend eradication
of H. pylori for the purpose of preventing gastric cancer (99). The NIH
conclusion was based upon the existence of clear examples of disparity in
the epidemiology of the two diseases. Gastric cancer is more common in
males than in females, whereas the rates of H. pylori infection are not
different for the two genders. Some populations are reported to have a high
rate of H. pylori infection but low rates of gastric cancer. Gastric cancer
occurs in some persons with no evidence of H. pylori infection, and in the
United States, fewer than 1% of H. pylori-infected persons will ever
develop gastric cancer. The strongest evidence that H. pylori is associated
with gastric cancer comes from three prospective studies that indicate that
H. pylori-infected persons have a significantly increased rate of gastric
cancer (96,98).
Only some retrospective serologic studies have shown an association. These
disparities indicate that factors other than H. pylori infection are also
important in gastric cancer risk. It is possible that only some strains of
H. pylori are involved in the carcinogenic process. For example, infection
with H. pylori strains possessing the cagA virulence factor is associated
with an increased risk of developing adenocarcinoma of the stomach
(100,101).
H. pylori is also associated with two less common forms of cancer,
non-Hodgkin lymphoma and mucosa-associated lymphoid tissue lymphomas of the
stomach (96). These types of lymphomas in the stomach only arise in the
setting of H. pylori inflammation. In 70% of H. pylori-infected patients
with lymphoma, treatment with appropriate antibiotics leads to regression
(96). This finding not only suggests a causal role but that treatment of a
bacterial infection can actually result in regression of cancer.
Another landmark study, published in June, 1997, shows that a 12-year
nationwide vaccination program against hepatitis B virus in Taiwan resulted
in a significant reduction in the number of cases of childhood liver cancer
(102). The role of chronic infection with hepatitis B virus in the etiology
of hepatocellular carcinoma is well established (103,104). Yet this is the
first evidence that prevention of a viral infection is also effective
against cancer. The implications are profound. Hepatitis B infection causes
some 316,000 cases of liver cancer (60% of all liver cancer) a year
worldwide (103,104). While hepatitis C causes a further 118,000 cases (22%
of all cases) a year (103,104), some cases result from infections with both
viruses (104).
The infectious origin of carcinoma of the cervix has long been suspected,
because known risk factors for the disease are linked to sexual activity
(105). Recent evidence indicates that human papillomavirus (HPV) types 16
and 18 are definitely carcinogenic in humans (94,105). Types 31 and 33 are
classified as probably carcinogenic (94,105). In the United States, HPVs,
are associated with 82% of the 15,000 cases and 4,600 deaths due to
cervical cancer each year. They are also associated with more than a
million precancerous lesions of varying severity. The combined direct
medical costs due to HPV are approximately 1.3 billion dollars per year in
the United States alone. Thus, effective therapy and vaccines would have a
major impact.
The pathogenic mechanisms by which infectious agents cause cancer have not
been resolved but they appear to be diverse. In cervical cancer, there
seems to be a clear role for HPV-encoded genes in tumor cell growth (106).
In addition to stimulation of cell proliferation, inactivation of tumor
suppressor genes, such as p53 may be a common pathway leading to malignancy
in HPV and hepatitis B virus (106,107). In the case of other viruses and H.
pylori, active oxygen and nitrogenic species generated by inflammatory
cells may cause DNA damage, induce apoptosis, and modulate enzyme
activities and gene expression (94,108).
Future Research Opportunities
The basic biology of agents implicated in chronic diseases and cancer, in
contrast to many other infectious agents, is relatively unknown. With rare
exception, the means by which pathogens suppress, subvert, or evade host
defenses and establish chronic or latent infection have received little
attention. Few areas of basic research compared with microbial latency hold
greater promise of substantially contributing to our understanding of
infectious diseases and the eventual relief of human suffering (109). Given
that the diseases discussed are among the most common in the world, even if
only some cases are proven to be of infectious origin and effective
therapies or vaccines can be developed, the impact on reducing health-care
costs would be substantial. Thus, further research to clarify the etiologic
agents and pathogenic mechanisms involved in chronic diseases and cancer
should be given the highest priority.
To address the potential role of infectious agents in chronic diseases
requires a new research paradigm compared to that which most investigators
and funding agencies in infectious diseases are accustomed. Such an
approach will require high levels of sustained funding of networks of
research groups (ideally at least for 10 years). The approach will require
collaborative research groups that follow a large number of well-defined
patients over long periods. Success will depend on involvement of
researchers highly skilled in clinical and epidemiologic investigation
supported by laboratory personnel with proven expertise in detection of a
wide spectrum of fastidious organisms. No single agent is likely to be the
cause of chronic obstructive lung disease, asthma, or cancer; rather a
number of infectious agents are likely to have this potential, hence the
need for studies of large numbers of patients. Because the infecting agent
may only be present in the very early stages of disease followed by an
inflammatory response, different stages of disease need to be studied. A
critical component of the investigative approach will be the ability to
determine the genetic background and immune response of the patients.
The randomized, controlled clinical trial provides a scientific experiment
that conforms to the standard model of biomedical research and is
undoubtedly the best theoretical approach to evaluating any new therapy
(110,111). Antibiotic treatment trials are commonly used to prove an
infectious etiology. While clinical trials are at their best in evaluating
the efficacy of therapies for acute diseases, clinical trials may not be
the best approach for evaluating the efficacy of therapies for chronic
diseases, most of which are likely to be complex, multifactorial illnesses
in which behavioral and lifestyle factors play an important role. Some of
the difficulties associated with this approach have already been discussed.
Well-defined, relevant animal models will be extremely important in
elucidating the role of infectious agents in chronic inflammatory diseases.
The animal studied should be the most genetically susceptible to the
infecting agent and chronic infection. All too often inappropriate
conclusions are based on use of a single strain of a single species. The
value of using a naturally occurring disease with features that closely
parallel those of the human disease cannot be overestimated.
As we attempt to prove the role of infection in chronic inflammatory
diseases and cancer, the biggest challenge will be convincing peer review
groups who establish research priorities and who facilitate funding
decisions that these are not "fishing expeditions." Likewise, the challenge
will be to convince journal editors that the findings are not merely
coincidental. To make rapid progress we must keep an open mind and accept
the likely possibility that fulfillment of Koch's postulates for infectious
agents involved in chronic inflammatory diseases and cancer may not be
possible.
Dr. Cassell is a recent past president of the American Society for
Microbiology, a member of the National Institutes of Health Director's
Advisory Committee, and a member of the Advisory Council of the National
Institute of Allergy and Infectious Diseases of NIH. She was named to the
original Board of Scientific Councilors of the National Center for
Infectious Diseases, CDC, and is the immediate past chair of the board.
Address for correspondence: Gail H. Cassell, Lilly Research Laboratories,
Lilly Corporate Center, Indianapolis, IN 46285, USA; fax: 317-276-1743;
e-mail: Cassell_Gail_H@Lilly.com.
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Bioterrorism as a Public Health Threat
D.A. Henderson
The Johns Hopkins University, Baltimore, Maryland, USA
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The threat of bioterrorism, long ignored and denied, has
heightened over the past few years. Recent events in Iraq,
Japan, and Russia cast an ominous shadow. Two candidate agents
are of special concern—smallpox and anthrax. The magnitude of
the problems and the gravity of the scenarios associated with
release of these organisms have been vividly portrayed by two
epidemics of smallpox in Europe during the 1970s and by an
accidental release of aerosolized anthrax from a Russian
bioweapons facility in 1979. Efforts in the United States to
deal with possible incidents involving bioweapons in the
civilian sector have only recently begun and have made only
limited progress. Only with substantial additional resources at
the federal, state, and local levels can a credible and
meaningful response be mounted. For longer-term solutions, the
medical community must educate both the public and policy
makers about bioterrorism and build a global consensus
condemning its use.
Until recently, biological terrorism had been little discussed or written
about. Until recently, I had doubts about publicizing the subject because
of concern that it might entice some to undertake dangerous, perhaps
catastrophic experiments. However, events of the past 12 to 18 months have
made it clear that likely perpetrators already envisage every possible
scenario.
Four points of view prevalent among national policy circles and the
academic community at various times have served to dismiss biological
terrorism as nothing more than a theoretical possibility. l) Biological
weapons have so seldom been deployed that precedent would suggest they will
not be used. 2) Their use is so morally repugnant that no one would deign
to use them. 3) The science of producing enough organisms and dispersing
them is so difficult that it is within the reach of only the most
sophisticated laboratories. 4) Like the concept of a "nuclear winter," the
potential destructiveness of bioweapons is essentially unthinkable and so
to be dismissed. Each of these arguments is without validity.
Nations and dissident groups exist that have both the motivation and access
to skills to selectively cultivate some of the most dangerous pathogens and
to deploy them as agents in acts of terrorism or war. After the Gulf War,
Iraq was discovered to have a large biological weapons program. In 1995,
Iraq confirmed that it had produced, filled, and deployed bombs, rockets,
and aircraft spray tanks containing Bacillus anthracis and botulinum toxin
(1,2); its work force and technologic infrastructure are still wholly
intact. Also in 1995, the Japanese cult, Aum Shinrikyo, released the nerve
gas Sarin in the Tokyo subway. The cult also had plans for biological
terrorism (3); included in its arsenal were large quantities of nutrient
media, botulinum toxin, anthrax cultures, and drone aircraft equipped with
spray tanks. Members of this group had traveled to Zaire in 1992 to obtain
samples of Ebola virus for weapons development.
Of more recent concern is the status of one of Russia's largest and most
sophisticated former bioweapons facilities, called Vector, in Koltsovo,
Novosibirsk. Through the early 1990s, this was a 4,000-person, 30-building
facility with ample biosafety level 4 laboratory facilities, used for the
isolation of both specimens and human cases. Situated on an open plain
surrounded by electric fences and protected by an elite guard, the facility
housed the smallpox virus as well as work on Ebola, Marburg, and the
hemorrhagic fever viruses (e.g., Machupo and Crimean-Congo). A visit in the
autumn of 1997 found a half-empty facility protected by a handful of guards
who had not been paid for months (P. Jahrling, pers. comm., 1998). No one
can say where the scientists have gone, nor is there confidence now that
this is the only storage site for smallpox virus outside the Centers for
Disease Control and Prevention.
The number of countries engaged in biological weapons experimentation has
grown from 4 in the 1960s to 11 in the 1990s (4). Meanwhile, the bombing of
the World Trade Center and the Oklahoma City Federal Building have
dramatized the serious problems even small dissident groups can cause.
A comprehensive review of the problems posed by biological terrorism and
warfare has been published (5). Four observations deserve special note.
First, biological terrorism is more likely than ever before and far more
threatening than either explosives or chemicals. Second, official actions
directed at the threat to the civilian population (less than 2 years in the
making) have been only marginally funded and minimally supported (6).
Third, preventing or countering bioterrorism will be extremely difficult.
Recipes for making biological weapons are now available on the Internet,
and even groups with modest finances and basic training in biology and
engineering could develop, should they wish, an effective weapon (7) at
little cost. Fourth, detection or interdiction of those intending to use
biological weapons is next to impossible. Thus, the first evidence of such
weapons will almost certainly be cases in hospital emergency rooms.
Specialists in infectious diseases thus constitute the front line of
defense. The rapidity with which they and emergency room personnel reach a
proper diagnosis and the speed with which they apply preventive and
therapeutic measures could spell the difference between thousands and
perhaps tens of thousands of casualties. Indeed, the survival of physicians
and health-care staff caring for the patients may be at stake. However,
today few have ever seen so much as a single case of smallpox, plague, or
anthrax, or, for that matter, would recall the characteristics of such
cases. Few, if any, diagnostic laboratories are prepared to confirm
promptly such diagnoses.
Of a long list of potential pathogens, only a handful are reasonably easy
to prepare and disperse and can inflict sufficiently severe disease to
paralyze a city and perhaps a nation. In April 1994, Anatoliy Vorobyov, a
Russian bioweapons expert, presented to a working group of the National
Academy of Sciences the conclusions of Russian experts as to the agents
most likely to be used (8). Smallpox headed the list followed closely by
anthrax and plague. None of these agents has so far effectively been
deployed as a biological weapon, and thus no real world events exist to
provide likely scenarios. However, we have had several well-documented
smallpox importations into Europe over recent decades; two bear recounting.
Smallpox is caused by a virus spread from person to person; infected
persons have a characteristic fever and rash. Virus infection invariably
results in symptomatic disease. There are no mild, subclinical infections
among unvaccinated persons. After an incubation period of 10 to 12 days,
the patient has high fever and pain. Then a rash begins with small papules
developing into pustules on day 7 to 8 and finally changing to scabs around
day 12. Between 25% and 30% of all unvaccinated patients die of the
disease. There was, and is, no specific treatment.
Until 1980, essentially all countries conducted vaccination programs of
some sort, whether or not they had endemic disease (9). Until 1972, the
United States mandated smallpox vaccination for all children at school
entry, although the last cases had occurred in 1949, 23 years before. In
the United Kingdom, four standby hospitals were to be opened only if
smallpox cases were imported, and in Germany, two state-of-the-art
isolation hospitals were constructed in the 1960s specifically for the
isolation of smallpox cases should they occur.
In 1962, the initial response of U.S. officials to the occurrence of a
single case of smallpox illustrated extreme concern. That year, a young
Canadian boy returned from Brazil, traveling by air to New York and by
train to Toronto by way of Albany and Buffalo (10). Shortly after arrival
in Toronto, he developed a rash and was hospitalized. In response to this
single case, senior U.S. government officials seriously considered a plan
of action that called for the border with Canada to be closed, for mass
vaccination campaigns to be conducted in all cities along the route from
New York through Albany, Syracuse, Rochester, and Buffalo, and for
vaccination of all who had been in Grand Central Station on the day the
Canadian boy was there. Sensibly, this plan was soon scrapped for more
modest measures, albeit not without considerable debate.
The potential of aerosolized smallpox to spread over a considerable
distance and to infect at low doses was vividly demonstrated in an outbreak
in Germany in 1970 (11). That year, a German electrician returning from
Pakistan became ill with high fever and diarrhea. On January 11, he was
admitted to a local hospital and was isolated in a separate room on the
ground floor because it was feared he might have typhoid fever. He had
contact with only two nurses over the next 3 days. On January 14 a rash
developed, and on January 16 the diagnosis of smallpox was confirmed. He
was immediately transported to one of Germany's special isolation
hospitals, and more than 100,000 persons were promptly vaccinated. The
hospital had been closed to visitors because of an influenza outbreak for
several days before the patient was admitted. After the diagnosis of
smallpox, other hospital patients and staff were quarantined for 4 weeks
and were vaccinated; very ill patients received vaccinia-immune globulin
first. However, the smallpox patient had had a cough, a symptom seldom seen
with smallpox; coughing can produce a large-volume, small-particle aerosol
like what might occur after its use as a terrorist weapon. Subsequently, 19
cases occurred in the hospital, including four in other rooms on the
patient's floor, eight on the floor above, and nine on the third floor. Two
were contact cases. One of the cases was in a visitor who had spent fewer
than 15 minutes in the hospital and had only briefly opened a corridor
door, easily 30 feet from the patient's room, to ask directions. Three of
the patients were nurses, one of whom died. This outbreak occurred in a
well-vaccinated population.
An outbreak in Yugoslavia in February 1972 also illustrates the havoc
created even by a small number of cases. Yugoslavia's last case of smallpox
had occurred in 1927. Nevertheless, Yugoslavia, like most countries, had
continued populationwide vaccination to protect against imported cases. In
1972, a pilgrim returning from Mecca became ill with an undiagnosed febrile
disease. Friends and relatives visited from a number of different areas; 2
weeks later, 11 of them became ill with high fever and rash. The patients
were not aware of each other's illness, and their physicians (few of whom
had ever seen a case of smallpox) failed to make a correct diagnosis.
One of the 11 patients was a 30-year-old teacher who quickly became
critically ill with the hemorrhagic form, a form not readily diagnosed even
by experts. The teacher was first given penicillin at a local clinic, but
as he became increasingly ill, he was transferred to a dermatology ward in
a city hospital, then to a similar ward in the capital city, and finally to
a critical care unit because he was bleeding profusely and in shock. He
died before a definitive diagnosis was made. He was buried 2 days before
the first case of smallpox was recognized.
The first cases were correctly diagnosed 4 weeks after the first patient
became ill, but by then, 150 persons were already infected; of these, 38
(including two physicians, two nurses, and four other hospital staff) were
infected by the young teacher. The cases occurred in widely separated areas
of the country. By the time of diagnosis, the 150 secondary cases had
already begun to expose yet another generation, and, inevitably, questions
arose as to how many other yet undetected cases there might be.
Health authorities launched a nationwide vaccination campaign. Mass
vaccination clinics were held, and checkpoints along roads were established
to examine vaccination certificates. Twenty million persons were
vaccinated. Hotels and residential apartments were taken over, cordoned off
by the military, and all known contacts of cases were forced into these
centers under military guard. Some 10,000 persons spent 2 weeks or more in
isolation. Meanwhile, neighboring countries closed their borders. Nine
weeks after the first patient became ill, the outbreak stopped. In all, 175
patients contracted smallpox, and 35 died.
What might happen if smallpox were released today in a U.S. city? First,
routine vaccination stopped in the United States in 1972. Some travelers,
many military recruits, and a handful of laboratory workers were vaccinated
over the following 8 years. Overall, however, it is doubtful that more than
10% to 15% of the population today has residual smallpox immunity. If some
modest volume of virus were to be released (perhaps by exploding a light
bulb containing virus in a Washington subway), the event would almost
certainly go unnoticed until the first cases with rash began to appear 9 or
10 days later. With patients seen by different physicians (who almost
certainly had never before seen a smallpox case) in different clinics,
several days would probably elapse before the diagnosis of smallpox was
confirmed and an alarm was sounded.
Even if only 100 persons were infected and required hospitalization, a
group of patients many times larger would become ill with fever and rash
and receive an uncertain diagnosis. Some would be reported from other
cities and other states. Where would all of these patients be admitted? In
the Washington, D.C., metropolitan area, no more than 100 hospital beds
provide adequate isolation. Who would care for the patients? Few hospital
staff have any smallpox immunity. Moreover, one or two patients with severe
hemorrhagic cases (which typically have very short incubation periods), who
would have been hospitalized before smallpox was suspected, would have been
cared for by a large, unprotected intensive care team.
What of contacts? In past outbreaks, contacts of confirmed or suspected
cases numbered in the thousands, if not tens of thousands. What measures
should or could be taken to deal with such numbers? Would patients be
isolated as in Yugoslavia, and if so, where? Logistics could be simplified
if rapid, easily used laboratory tests could confirm or rule out smallpox
among suspected cases. At present, however, such tests are known only to
scientists in two government laboratories.
An immediate clamor for mass vaccination (as in the outbreaks in Germany
and Yugoslavia) can be predicted. U.S. stocks of smallpox vaccine are
nominally listed at 15 million doses, but with packaging, the useful number
of doses is perhaps half that number. How widely and quickly should this
vaccine be used? Were vaccine to be limited strictly to close contacts of
confirmed cases, comparatively few doses would be needed. However, the
realities of dealing with even a small epidemic would almost certainly
preclude such a cautious, measured vaccination effort. Vaccine reserves
would rapidly disappear, and there is, at present, no manufacturing
capacity to produce additional vaccine. If an emergency effort were made to
produce new stocks of smallpox vaccine, many months to a year or more would
be required.
What of anthrax, which has been so enthusiastically embraced by both Iraq
and the Aum Shinrikyo? The organism is easy to produce in large quantity.
In its dried form, it is extremely stable. The effect of aerosolized
anthrax on humans once had to be inferred from animal experiments and the
occasional human infection among workers in factories processing sheep and
goat hides (12). It was clear that inhalation of anthrax is highly lethal.
Just how lethal became evident in the 1979 Sverdlovsk epidemic (13).
In all, 77 cases were identified with certainty; 66 patients died. The
actual total number of cases was probably considerably more than 100. The
persons affected lived or worked somewhere within a narrow zone extending
some 4 km south and east of a military bioweapons facility. An accidental
airborne release of anthrax spores occurred during a single day and may
well have lasted no more than minutes. Further investigations revealed
anthrax deaths among sheep and cows in six different villages up to 50 km
southeast of the military compound along the same axis as the human cases.
Of the 58 patients with known dates of disease onset, only 9 had symptoms
within a week after exposure; some became ill as late as 6 weeks after
exposure. Whether the onset of illness occurred sooner or later, death
almost always followed within 1 to 4 days after onset. However, there
appeared to be a somewhat higher proportion of survivors after the fourth
week. This almost certainly resulted from the widespread application of
penicillin prophylaxis and anthrax vaccine, both of which were distributed
in mid-April throughout a population of 59,000.
Meselson and his colleagues, who documented this outbreak, calculate that
the weight of spores released as an aerosol could have been as little as a
few milligrams or as much as "nearly a gram." Iraq acknowledged producing
at least 8,000 L of solution with an anthrax spore and cell count of 109/ml
(1). The ramifications of even a modest-sized release of anthrax spores in
a city are profound. Emergency rooms would begin seeing a few patients with
high fever and some difficulty breathing perhaps 3 to 4 days after
exposure. By the time the patients were seen, it is almost certain that it
would be too late for antibiotic therapy. All patients would die within 24
to 48 hours. No emergency room physicians or infectious disease specialists
have ever seen a case of inhalation anthrax; medical laboratories have had
virtually no experience in its diagnosis. Thus, at least 3 to 5 days would
elapse before a definitive diagnosis would be made.
Once anthrax was diagnosed, one would be faced with the prospect of what to
do over the succeeding 6 to 8 weeks. Should vaccine be administered to
those who might have been exposed? At present, little vaccine is available,
and no plan exists to produce any for civilian use. Should antibiotics be
administered prophylactically? If so, which antibiotics, and what should be
the criteria for exposure? What quantity would be required to treat an
exposed population of perhaps 500,000 over a 6-week period? Should one be
concerned about additional infections resulting from anthrax spores
subsequently resuspended and inhaled by others? Should everyone who has
been anywhere near the city report to a local physician for treatment at
the first occurrence of fever or cough, however mild? Undoubtedly, many
would have such symptoms, especially in the winter; how can such symptoms
be distinguished from the premonitory symptoms of anthrax that may proceed
to death within 24 to 48 hours?
We are ill-prepared to deal with a terrorist attack that employs biological
weapons. In countering civilian terrorism, the focus (a modest extension of
existing protocols to deal with a hazard materials incident) has been
almost wholly on chemical and explosive weapons. A chemical release or a
major explosion is far more manageable than the biological challenges posed
by smallpox or anthrax. After an explosion or a chemical attack, the worst
effects are quickly over, the dimensions of the catastrophe can be defined,
the toll of injuries and deaths can be ascertained, and efforts can be
directed to stabilization and recovery. Not so following the use of
smallpox or anthrax. Day after relentless day, additional cases could be
expected, and in new areas.
The specter of biological weapons use is an ugly one, every bit as grim and
foreboding as that of a nuclear winter. As was done in response to the
nuclear threat, the medical community should educate the public and policy
makers about the threat. We need to build on the 1972 Biological and Toxin
Weapons Convention to strengthen measures prohibiting the development and
production of biological weapons and to ensure compliance with existing
agreements. In a broader sense, we need a strong moral consensus condemning
biological weapons.
But this is not enough. In the longer term, we need to be as prepared to
detect, diagnose, characterize epidemiologically, and respond appropriately
to biological weapons use as to the threat of new and reemerging
infections. In fact, the needs are convergent. We need at international,
state, and local levels a greater capacity for surveillance; a far better
network of laboratories and better diagnostic instruments; and a more
adequate cadre of trained epidemiologists, clinicians, and researchers.
On the immediate horizon, we cannot delay the development and
implementation of strategic plans for coping with civilian bioterrorism.
The needed stocking of vaccines and drugs as well as the training and
mobilization of health workers, both public and private, at state, city,
and local levels will require time. Knowing well what little has been done,
I can only say that a mammoth task lies before us.
D.A. Henderson is a distinguished service professor at the Johns Hopkins
University, with appointments in the Departments of Health and
Epidemiology, School of Hygiene and Public Health. Dr. Henderson directed
the World Health Organization's global smallpox eradication campaign
(1966-1977) and helped initiate WHO's global program of immunization in
1974. He also served in the federal government as deputy assistant
secretary and senior science advisor in the Department of Health and Human
Services.
References
1. Ekeus R. Iraq's biological weapons programme: UNSCOM's experience.
Memorandum report to the United Nations Security Council; 1996 20 Nov;
New York.
2. Zalinskas RA. Iraq's biological weapons: the past as future? JAMA
1997;278:418-24.
3. Daplan E, Marchell A. The cult at the end of the world. New York:
Crown Publishing Group; 1996.
4. Roberts B. New challenges and new policy priorities for the 1990s. In:
Biologic weapons: weapons of the future. Washington: Center for
Strategic and International Studies; 1993.
5. Bioweapons and bioterrorism. JAMA 1997;278:351-70, 389-436.
6. Tucker JB. National health and medical services response to incidents
of chemical and biological terrorism. JAMA 1997;285:362-8.
7. Danzig R, Berkowsky PB. Why should we be concerned about biological
warfare? JAMA 1997;285:431-2.
8. Vorobyov A. Criterion rating as a measure of probable use of bio
agents as biological weapons. In: Papers presented to the Working
Group on Biological Weapons Control of the Committee on International
Security and Arms Control, National Academy of Sciences; 1994 Apr;
Washington.
9. Fenner F, Henderson DA, Arita I, Jezek Z, Ladnyi I. Smallpox and its
eradication. Geneva: World Health Organization; 1988.
10. Epidemiologic report. Smallpox, Canada. MMWR Morb Mortal Wkly Rep
1962;11:258.
11. Wehrle PF, Posch J, Richter KH, Henderson DA. An airborne outbreak of
smallpox in a German hospital and its significance with respect to
other recent outbreaks in Europe. Bull World Health Organ
1970;4:669-79.
12. Brachman PS, Friedlander AM. Anthrax. In: Plotkin SA, Mortimer EA,
editors. Vaccines. Philadelphia: WB Saunders; 1994.
13. Meselson M, Guillemin V, Hugh-Jones M, Langmuir A, Popova I, Shelokov
A, et al. The Sverdlovsk anthrax outbreak of 1979. Science
1994;266:1202-8.
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Bioterrorism as a Public Health Threat
Joseph E. McDade* and David Franz‡
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; ‡U.S.
Army Medical Research Institute of Infectious Diseases, Ft. Detrick,
Maryland, USA
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In addition to meeting the continuing threat of new and reemerging
infectious diseases, public health officials must also prepare for the
possible use of infectious agents as weapons by terrorists to further
personal or political agendas. These were the conclusions of session
panelists Scott Lillibridge, Centers for Disease Control and Prevention
(CDC); Michael Skeels, Oregon State Public Health Laboratory; Marcelle
Layton, New York City Department of Public Health; David Franz, U.S. Army
Medical Research Institute of Infectious Diseases; and Randall Murch,
Federal Bureau of Investigation (FBI).
The potential spectrum of bioterrorism ranges from hoaxes and use of
nonmass casualty devices and agents by individuals and small groups to
state-sponsored terrorism that employs classic biological warfare agents
and can produce mass casualties. The agents of anthrax, plague,
brucellosis, smallpox, viral encephalidites, and viral hemorrhagic fevers
are of particular concern: they are relatively easy and inexpensive to
produce, cause death or disabling disease, and can be aerosolized and
distributed over large geographic areas. If released under ideal
environmental circumstances, these agents can infect hundreds of thousands
of persons and cause many deaths. Such scenarios would present serious
challenges for patient management and for prophylaxis of exposed persons;
environmental contamination could provide a continuing threat to the
population (especially those exposed at the beginning of the crisis) and
generate panic in the community.
Bioterrorist attacks could be covert or announced and could be caused by
virtually any pathogenic microorganism. The case of the Rajneeshee
religious cult in The Dalles, Oregon, is an example (1). The cult planned
to infect residents with Salmonella on election day to influence the
results of county elections. To practice for the attack, they contaminated
salad bars at 10 restaurants with S. Typhimurium on several occasions
before the election. A communitywide outbreak of salmonellosis resulted; at
least 751 cases were documented in a county that typically reports fewer
than five cases per year. Although bioterrorism was considered a
possibility when the outbreak was being investigated by public health
officials, it was considered unlikely. The source of the outbreak became
known only when FBI investigated the cult for other criminal violations. A
vial of S. Typhimurium identical to the outbreak strain was found in a
clinical laboratory on the cult's compound, and members of the cult
subsequently admitted to contaminating the salad bars and putting
Salmonella into a city water supply tank. This incident, among other recent
events, underscores the importance of improving preparedness at all levels.
A bioterrorist attack may be difficult to distinguish from a naturally
occurring infectious disease outbreak. Investigators must first examine the
etiology and epidemiology of an outbreak to identify its source, mode of
transmission, and persons at risk. Certain clues may indicate whether an
outbreak is the result of purposeful release of microorganisms. Naturally
occurring diseases are endemic to certain areas and involve traditional
cycles of transmission; some diseases occur seasonally, and sentinel cases
are not uncommon. In contrast, a disease outbreak due to bioterrorism could
occur in a nonendemic-disease area, at any time of year, without warning,
and depending on the etiologic agent and mode of transmission, in large
numbers—thousands of cases might occur abruptly. Public health officials
must be appropriately sensitized to the possibility of bioterrorism when
investigating disease outbreaks. Suspected bioterrorism should be reported
promptly to FBI, which is responsible for coordinating interagency
investigations of such episodes. FBI scientists are also well trained in
forensic methods for criminal investigations and are prepared to react
quickly and effectively.
Maintaining effective disease surveillance is an essential first step in
preparedness and is important in helping law enforcement officials to react
swiftly. Ensuring adequate epidemiologic and laboratory capacity nationwide
are prerequisites to effective surveillance systems. Preparations also must
include plans for rapid identification and characterization of agents
involved and for emergency distribution of large quantities of medical
supplies, especially antibiotics and vaccines. Coordination and
communication links also need to be strengthened to minimize response time,
especially at first when exposed but asymptomatic persons may still be
treated prophylactically. Also, when response time is shortened, the
possibility of apprehending perpetrators increases. Education and training
in bioterrorism and its potential consequences must become national
priorities.
Many agencies and organizations must work collaboratively to ensure national
preparedness against bioterrorist attacks. CDC is well positioned to provide
leadership in several areas. In partnership with state health departments, the
agency maintains infectious disease surveillance systems and provides
reference laboratory diagnosis and epidemiologic support, especially during
outbreak investigations; disseminates public health recommendations and other
information, issues quarantine measures, and provides expert advice on worker
health and safety; and is the logical bridge between the public health
community and FBI's scientific and response capabilities. Enhancing the public
health infrastructure will improve U.S. ability to respond to any infectious
disease outbreak and provide added value in the event of a bioterrorist event.
[photo]
References
1. Torok TJ, Tauxe RV, Wise RP, Livengood JR, Sokolow R, Mauvais S, et
al. A large community outbreak of salmonellosis caused by intentional
contamination of restaurant salad bars. JAMA 1997;278:389-95.
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Who Speaks for the Microbes?
Stanley Falkow
Stanford University School of Medicine, Stanford, California, USA
------------------------------------------------------------------------
In discussing emerging infectious diseases, the focus is often on the
clinical effects of the host-parasite relationship, i.e., the impact on the
health and survival of humans and animals, rather than the examination of
the biology of the pathogen. It seems fitting to take a moment to reflect
on how pathogens "got that way in the first place." Thus, while we discuss
emerging infections, it is worthwhile to consider that from the beginning
of recorded history—in books or the pictographs of ancient
culturesinfectious diseases have been the leading cause of illness and
death. Even today, because of infectious diseases most of the world's
population does not have the luxury of living long enough to succumb to the
chronic diseases of aging.
What were and what remain the reasons that infectious diseases are still
the leading cause of death? I believe there are four answers. 1) The
presence of human populations was and is large enough to sustain and
amplify parasites. We have lived in communities large enough to perpetuate
parasites for only about 10,000 years, barely a blink of the eye in the
time frame of evolution, which means that most of the well-known infectious
diseases adapted to humans are very recent in the evolutionary sense. The
black death of the 14th century, just 700 years ago, led to the death of
approximately one quarter to one third of the human population of what was
then the Western world. We may never understand the full implications of
the plague outbreaks of the Middle Ages. The resistance of some caucasian
populations to the recent scourge of HIV actually may reflect the genetic
consequences of plague survival 20 generations ago. 2) Poverty, with its
crowding, unsanitary conditions, and often malnutrition, has led to an
increased susceptibility to infection and disease. 3) War, famine, civil
unrest, and, indeed, epidemic disease have led to a breakdown in public
infrastructure and the increased incidence of infectious diseases. 4) The
domestication of animals, beginning about 12,000 years ago, was another
important factor. The actual large-scale domestication of animals has
slowed and has been replaced by the encroachment of human populations into
the domain of animal species all over the globe. It is little wonder that
our deliberate destruction of predators and the outgrowth of human
populations into virgin land with its attendant destruction of habitat led
to the emergence of new diseases such as Lyme disease and murine typhus
(spread now by opossums and cat fleas in our slums, instead of by the more
classic rat and rat flea vector—"sic transit gloria mundi").
The Enemy Is Us
The cartoon character Pogo, invented by Walt Kelly, once announced to his
companions that "the enemy is us." I believe that many of what we refer to
as emerging diseases are characterized better as "diseases of human
progress." Thus, many major public health crises of the past 2 decades have
been infectious in origin. Many, like the outbreaks of Lyme disease and
murine typhus, are a natural consequence of human meddling. Similarly, the
appearance of infections, like Legionnaires' disease, can be traced to more
subtle differences in human behavior and social conventions that have an
effect on the microbial world. Thus, the aerosolization of water, now so
prominent in the Western world from the widespread use of showers instead
of baths to the spraying of produce in large markets to air conditioning,
likely has played an important role in the emergence of Legionnaires'
disease and also of Mycobacterium avium infection in both healthy and
immunocompromised persons.
Legionella pneumophila, the Legionnaires' bacillus, is found in nature as
an infectious agent of predatory protozoa. Introduction of this organism,
often as part of an aerosol of potable water into the alveolus of the lung,
results in the microorganism's finding a new niche in the macrophage
instead of in its usual host Acanthamoeba or Hartmanella. More absorbent
tampons helped select for a new disease, toxic shock syndrome.
While pathogenic traits of the disease-causing microbes are of consequence,
humans and their technology and social behavior have played a major role in
providing pathogenic microbes with new venues for their wares. Food
poisoning by Escherichia coli O157, Campylobacter, and Salmonella emerged
more from food technology and food distribution networks than from any
fundamental change in the virulence properties of the bacteria. In a sense,
we have provided these bacteria with a moveable feast.
What Is a Pathogen, Anyway?
Medicine views pathogens as microorganisms capable of causing disease. The
emphasis is on disease, not the microorganism. However, from the microbial
standpoint, being pathogenic is a strategy for survival and simply one more
remarkable example of the extraordinary diversity of the microbial world.
Humans are a home to a myriad of other living creatures. From mouth to
anus, from head to toes, every millimeter of our cells exposed to the
outside world is inhabited by a rich biology. From the mites that may
inhabit the eyebrows to the seething cauldron of more than 600 species of
bacteria that inhabit the large bowel, we are a veritable garden of
microorganisms. Most of these microorganisms are not only innocuous but
play a useful, yet unseen, role in our lives. They protect against the few
harmful microorganisms that we encounter each day; they provide vitamins
and nutrients and help digest food. We have harbored them so long in our
evolution that they are even a necessary part of the developmental pathways
required for the maturation of intestinal mucosa and the immune system.
Most microbes are commensal; that is, they "eat from the same table."
Others are either commensal or transient microbes that are opportunistic;
they can cause disease if one (or more) usual defense mechanism, evolved to
restrict microorganisms from normally sterile inner organs and tissue, is
breached by accident, by intent (as in surgery and, increasingly, in
gunshot wounds), or by an underlying metabolic or even infectious disorder.
Nevertheless, a small group of microorganisms often causes infection and
overt disease in seemingly healthy persons.
Many of the microorganisms, for example, the typhoid bacillus, gonococcus,
tubercle bacillus, and treponema of syphilis, are adapted exclusively to
humans; others, for example, Salmonella Typhimurium, can regularly cause
disease in humans, animals, birds, and reptiles. The distinct difference
between commensal, opportunistic, and pathogenic microbes is that
pathogenic microbes have evolved the genetic ability to breach cellular and
anatomic barriers that ordinarily restrict other microorganisms. Thus,
pathogens can inherently cause damage to cells to forcefully gain access to
a new, unique niche that provides them with less competition from other
microorganisms, as well as with a ready new source of nutrients.
For microorganisms that inhabit mammals as an essential component of their
survival tactic, success can be measured by their capacity to multiply
sufficiently to be maintained or be transmitted to a new susceptible host.
This is true for commensal and pathogenic organisms alike. However, if the
pathogen gains a new niche free of competition and rich in nutrients, it
also faces a more hostile environment designed by evolution to restrict
microbial entry and, indeed, to destroy any intruders that enter these
protected regions. Thus, pathogens have not only acquired the capacity to
breach cellular barriers but also, by necessity, have learned to
circumvent, exploit, and subvert our normal cellular mechanisms for their
own selfish need to multiply at our expense.
How Did Pathogens Get That Way?
Recent advances in bacterial genetics, molecular biology, and microbial
genomics have led to a better understanding of the evolution of bacterial
pathogenicity. In genera that have both pathogenic and nonpathogenic
organisms, the nonpathogenic bacteria frequently possess one (or more)
large genetic insert that contains genes exclusively associated with the
pathogenic phenotype. Indeed, in gram-negative enteric bacteria, pathogenic
traits are commonly found as large inserts of DNA in the chromosome, as are
plasmids dedicated to the pathogenicity of the host microbe. Certain
qualities of these DNA inserts suggest that they were acquired by
horizontal gene transfer from one microbe to another and that the ultimate
origin of these virulence genes was a microbe very different from the
organism in which these genes now reside. These "pathogenicity islands"
have been the subject of a number of recent articles. However, the
evolution of pathogenicity is not the product of a slow, plodding process
as much as it is the product of a large single genetic event that had a
profound influence on the biology of the microorganism. Thus, the
divergence of Salmonella from an ancestor that also gave rise to E. coli
resulted when the organism received a large pathogenicity island that
encoded a contact-dependent secretory system, which gave the host bacterium
the ability to cross epithelial barriers. Later on in evolution, some
Salmonellae received another pathogenicity island that provided the host
bacterium with the ability to survive within phagocytic macrophages;
finally, other Salmonellae that infect only warm-blooded animals eventually
inherited a plasmid that appears to permit systemic spread and, perhaps,
some degree of host animal preference. These genetic events occurred over
millions of years of evolution and were undoubtedly rare, perhaps occurring
only once in evolution.
The success of these genetic changes also depended on subsequent selective
pressures and genetic fine-tuning by mutation and other genetic mechanisms.
Nevertheless, the molecular fossil record in the DNA of contemporary
pathogens leads to the inevitable conclusion that microbial evolution is
still dynamic and that these periodic genetic upheavals in microbes
affecting their pathogenicity can occur at any time. To underestimate the
evolutionary potential of microorganisms and their ability to survive, even
in the face of enormous pressures to eradicate them and their effects on
humankind, would be a mistake.
Infectious agents will emerge so long as there are microorganisms. Humans
help the evolutionary process sometimes unwittingly and sometimes by arrogance
or ignorance. Antibiotic resistance on a global scale in what seems such a
short time comes as no surprise. Does feeding animals antibiotics to promote
growth have any effect on human microbes and the health of the human population
as a whole?
Rachel Carson's book Silent Spring, which documents the devastating effects
of insecticides (e.g., DDT) on the health of a number of living creatures
far removed from the insects that were the target, was easily understood.
Yet, application of a selective pressure on the microbes of the planet with
antibiotics, a pressure that dwarfs the use of DDT in its scope, as well in
the number of species that are affected, still remains a subject of debate
after 50 years. Is it because we could see the effects of DDT in the
pictures of fragile eagle eggs but not in the unseen microscopic world? As
Pasteur said, the microbe will endure. Perhaps the fate of the last human
is to be consumed by its own microorganisms.
Suggested Bibliography
1. Bäumler AJ. The record of horizontal gene transfer in Salmonella.
Trends Microbiol 1997;5:318-22.
2. Falkow S. The evolution of pathogenicity in Escherichia, Shigella, and
Salmonella. In: Neidhardt F, editor. Escherichia coli and Salmonella:
cellular and molecular biology. Washington: American Society for
Microbiology; 1995. p. 2723-9.
3. Finlay BB, Cossart P. Exploitation of mammalian host cell functions by
bacterial pathogens. Science 1997;276:718-25.
4. Galán JE, Bliska JB. Cross-talk between bacterial pathogens and their
host cells. Ann Rev Cell Dev Biol 1996;12:221-55.
5. Groisman EA, Ochman H. How Salmonella became a pathogen. Trends
Microbiol 1997;5:343-9.
6. Hacker J, Blum-Oehler G, Muhildorfer I, Tachape H. Pathogenicity
islands of virulent bacteria: structure, function and impact on
microbial evolution. Mol Microbiol 1997;23:1089-97.
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Emerging Diseases What Now?
George A. O. Alleyne
Pan American Health Organization, Washington, D.C., USA
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The Pan American Health Organization (PAHO) was born in 1902 out of concern
for the spread of infectious diseases. The outbreak of cholera in Hamburg
in 1892 and the epidemics of yellow fever in the Americas led to the
decision to establish the International Sanitary Bureau with permanent
headquarters in Washington. At the conference that made this historic
decision in 1902, participating countries agreed to cooperate with each
other and transmit to the bureau "all data of every character relative to
the sanitary conditions of their ports and territories and furnish said
Bureau every opportunity and aid for a thorough and careful study and
investigation of any outbreaks of pestilential disease." All this was to be
done to provide the "widest possible protection of the public health of
each of the said republics and that commerce between said republics may be
facilitated."
To a very large extent, we are still following the bureau's
recommendations, only the list of pestilential diseases is shorter by one.
Smallpox is no longer with us–and cholera, yellow fever, and bubonic plague
are now among the emerging diseases. Cholera is far from disappearing.
There were approximately 400,000 cases in the Americas in 1991. This number
fell to 18,000 in 1997, but recent reports indicate that as a result of
flooding caused by El Niño, the number of cases in Peru has increased
dramatically this year. For the first 4 weeks of this year, 2,863 cases
were reported compared with 174 for the same period last year and 3,500 for
the whole of 1997.
Over the past 5 years, emerging diseases have caused intense concern and
activity. The growth in international travel is a major factor. Statistics
from the World Tourism Organization show that some 1 million persons per
day traveled from their homes by air in 1995. International travel has
increased every one of the past 10 years with an average increase of 5.5%
per annum. Approximately 1.6 million people cross or recross the
U.S.-Mexico border every day by land. Cholera did not spread between the
Peruvian towns of Chancay and Chimbote by air travel, but by normal
intercity traffic.
The spread of antibiotic resistance is another reason for the emergence of
disease; the indiscriminate use of antibiotics is to blame. In the South,
antibiotic abuse is facilitated by ready availability without a
prescription. In some countries, local pharmacies stock and dispense
antibiotics with the same facility as they do cough syrups. In one study of
private pharmacies, 42% of the antibiotics were dispensed without
prescription (1); in another study, only 23% were given with a physician's
prescription (2).
The essential elements of a control strategy for addressing emerging
infections are a surveillance system, strengthening the public health
infrastructure (including enhancing laboratory capability), stimulation of
research, and training of personnel. This strategy is difficult. However, a
review of past surveillance activities provides specific lessons.
At the regional level, three disease surveillance systems (for
foot-and-mouth disease, poliomyelitis, and measles) have worked and are
working. An essential common feature is that surveillance leads to
definitive action. For example, detection of cases of poliomyelitis (before
the disease was finally eliminated from the Americas) automatically
triggered a response. The report of a suspected case now causes resources
to be mobilized to establish the validity of the report.
In addition, strong motivation undergirds surveillance. In the case of
animal vesicular disease, there is the intense commercial interest behind
the maintenance of the system and the possibility of eradication of
foot-and-mouth disease. The commercial interest arises because elimination
of the disease from the countries of the South represents a possibility of
exporting beef worth billions of dollars. Interest rests not only with the
national authorities; small communities actually drive the system. An
estimated 70% of the cattle are owned by peasants, who each own 10 or
fewer. Systematic regular feedback is necessary to maintain interest.
The surveillance systems for these diseases are based on the use of
geographic coordinates to divide the countries into grids that represent
the special unit in which the data are collected. Reports are sent by the
local veterinary service to the Pan American Foot-and-Mouth Disease Center
in Brazil. In recent years, a system has been developed for childhood
illnesses that is as sensitive as that which reports animal diseases. The
driving force behind the successful development and maintenance of the
surveillance system for these childhood illnesses is the possibility of a
finite end–eradication and the emotional pride that national health workers
and politicians have in reaching this end.
Perhaps the most important aspect of successful surveillance systems is the
presence of a credible coordinating international body. No effective
international surveillance system can be mounted by a single country, no
matter how well it is endowed. External energy, commitment, expertise, and
persistence are necessary for such systems to function.
The technology of communication should not become the focus of our efforts.
The surveillance and containment systems for smallpox depended on
telegrams, telexes, and, I suspect, talking drums. "In India, the largest
of the endemic countries, there were no fewer than 8,167 units reporting
weekly to 397 district offices, which in turn reported to 31 state program
offices and those to the national program office in New Delhi" (3). All
this and more was sent to Geneva to be analyzed and reported back
faithfully, without the benefit of electronic mail. New information
technology is not an indispensable part of the solution.
It is challenging to our sense of superiority as a species to realize that
diseases will always emerge. Changes in our social and physical ecology
will almost certainly ensure the emergence of new or old diseases, and we
are now more vulnerable to these diseases than before. Thus, strategies and
policies must be able to be adapted to confront the inevitable new threats;
the international community must avoid the peaks and valleys of action that
accompany public interest in the exotic.
We have already begun to implement agreed-upon strategies in one particular
area. To establish a system for surveillance of antibiotic resistance to
enteric pathogens, we identified participating laboratories in 14 countries
of the Americas. The next step was to standardize isolation techniques and
review methods for measuring antibiotic sensitivity. We are applying an
approach similar to the one that proved successful with the Pan American
Regional Poliomyelitis Laboratory Network and have adopted "open
regionalism"—establishing limited networks that may expand eventually and
cooperate among themselves.
PAHO is also creating a functional network of laboratories in the greater
Amazon Region to provide data on emerging infections. The participating
laboratories' common objective will be the provision of accurate results,
prompt sharing of information and research protocols, and a mechanism for
rapid transfer of technology. However, the laboratories will need external
support to sustain the system.
A strong global system for the application of strategies to control
emerging diseases will not occur if the agreement on global action exists
only in the sphere of surveillance. There is a fundamental need for other
health professionals, in addition to microbiologists, to be convinced of
the need for a global approach to some health issues.
The fear of infectious disease has been a powerful stimulus for global
action. The successful global system for influenza is due partly to the
coordinating efforts of the World Health Organization (WHO) and the work of
the key collaborating laboratory centers. Involvement in these efforts
keeps laboratories abreast of the latest developments in their special
fields.
The need for global health coordination has been very much in the news; the
appropriate body to perform that function is WHO. Most nations agree that
they must assume responsibility for what are called essential public goods,
e.g., immunization, provision of clean water. But some goods are public
beyond national considerations, and no single nation can coordinate the
availability of these international public goods.
International leadership goes beyond emerging diseases; indeed the success
of a global effort to address the threat of these diseases depends largely
on the wider perception of responsibilities for global coordination in
health. Some believe that the global effort must focus on problems more
common in the developing world and that global coordination is a mechanism
for channeling resources from the rich to the less fortunate. However, all
countries need to appreciate the benefits of global coordination of efforts
such as those needed to address emerging diseases. Multilateralism is not
antithetical to national interests or bilateral approaches. Success of this
multilateral approach will require budgetary support. The annual regular
budget of WHO is approximately US$420 million—14% of PAHO's budget. As
Joshua Lederberg said, "Our thinking has been impoverished in terms of
budget allocation for dealing with health on an international basis."
Some very successful efforts at global coordination in health have been
disease or theme specific, and the "Special Program" approach has given
some very good results. However, we should go beyond that and have a global
health forum or council in which those agencies and institutions active or
becoming increasingly active in health join with WHO in determining how to
coordinate the various efforts. I would include in this forum
representation from the multilateral financial institutions, the private
sector, and nongovernmental organizations. Different spheres of interest
and action would complement each other, which should help correct the
current ad hoc theme-driven approach that continues to draw criticism.
PAHO has emphasized the benefit of a collective approach, and
Panamericanism is one of the major underlying principles of the
organization's work. For example, "Health Technology Linking the Americas,"
a concept that promotes the availability of simple effective technologies
throughout the Americas, is a current initiative. Vaccines are one of the
technologies emphasized.
In conclusion, we must promote the individual study of the nature and local
means of control of emerging diseases. However, we also need a more
collective approach at the regional, or even better, the global level this
approach is bound up with the support for global action on other fronts in
health. The most powerful instrument we have is multipronged
advocacy advocacy is needed at the political and popular levels for this
approach. The public must be engaged on a more regular basis to consider
the truism that public health must be a concern of the public. This
advocacy has to use some specific examples of those matters that affect the
public's health so that emerging diseases are not seen as a threat only on
television.
References
1. Brieva J, Danhier A, Villegas G, Yates T, Pérez H. Modalidades del uso
de antibióticos en Concepción, Chile. Boletín Oficina Sanitaria
Panamericana 1987;103(4):363-72.
2. López R, Kroeger A. Morbilidad y medicamentos en Perú y Bolivia.
Universidad Peruana, Cayetano Heredia, Lima, Perú. Acción para la
salud, Chimbote, Perú. Ministerio de Salud, La Paz, Bolivia.
Universidad de Heidelberg, Alemania, 1990.
3. Fenner F, Henderson DA, Arita I, Jezek Z, Ladnyi ID. Smallpox
and its eradication. Geneva: World Health Organization; 1988. p. 497.
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Letters
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Outbreak of Suspected Clostridium butyricum Botulism in India
To the Editor: Foodborne botulism, particularly associated with Clostridium
butyricum, is rare; no cases had been reported in India before this
outbreak. A reported case of foodborne botulism represents a public health
emergency because of the potential severity of the disease and the
possibility of mass exposure to the contaminated product.
In September 1996, the anaerobic section of the All India Institute of
Medical Sciences received serum and food samples from the National
Institute of Communicable Diseases, Delhi, India, for investigating a
possible outbreak of foodborne botulism.
In the early hours of September 18, 1996, 34 of 310 students of a
residential school in rural Gujrat complained of abdominal pain, nausea,
chest pain, and difficulty in breathing. One of the students, aged 14, died
before he could be treated; two others, aged 13, died on their way to the
hospital. The remaining 31 students were admitted to a rural hospital;
eight were discharged 1 day later after being given symptomatic treatment,
while the other 23 were transported by ambulance to an urban emergency
department in Ahemdabad, Gujrat. Findings on examination included ptosis,
pupillary mydriasis, extraocular palsies, and impairment of conciousness.
All students were given symptomatic treatment in the form of stomach lavage
and intravenous administration of antibiotics and steroids. Over the
subsequent 24 hours, 21 improved clinically and were discharged; however,
two (aged 14 and 17 years) had respiratory distress and required mechanical
ventilation. Differential diagnosis included botulinum food poisoning, and
both patients were administered trivalent (A,B,E) botulinum antitoxin. They
responded well to the treatment and were discharged from the hospital 1
month later.
Patients reported that 24 hours before onset of symptoms, they had eaten
ladoo (a local sweet), curd, buttermilk, sevu (crisp made of gram flour),
and pickle. Food samples were assayed for botulinum toxin and were cultured
anaerobically (1). Anaerobic culture of leftover sevu yielded an organism
in pure culture whose cultural and biochemical properties were consistent
with those of C. butyricum; i.e., it was lipase-negative, fermentative, and
did not liquefy gelatin (2). Enrichment cultures of the sevu specimens in
enriched chopped meat-glucose-starch medium contained toxin after 5 days of
anaerobic incubation at 30°C. This was shown by mouse toxicity test in
which the enrichment broth of the specimen was injected intraperitoneally
into mice; botulinum toxin was detected by observing its lethal effect on
mice. This effect was neutralized by specific polyvalent botulinum
antitoxin types A, B, E (Biomed, Warsaw, Poland). Cultures of other food
items tested negative for toxigenic organisms. Serum specimens (obtained
more than 1 week after the onset of illness) from eight patients with
mildly symptomatic illness were negative for toxin.
To test the presence of toxin gene in the isolated strain of C. butyricum,
polymerase chain reaction (PCR) was performed. Degenerate primers BoNT 1
and BoNT 2 were used, which amplify a specific 1.1-kb fragment of
neurotoxin gene C. botulinum types (A, B, E, F, and G) as well as toxigenic
strains of C. baratti and C. butyricum (3). Five Escherichia coli strains
containing clones encoding fragments of the C. botulinum neurotoxin genes
were used as positive controls in the PCR assay (kindly provided by Alison
East, Institute of Food Research, United Kingdom). PCR profile used was as
follows: 94°C for 2 min, followed by 25 cycles of 92°C for 1 min, 42°C for
1 min, and 62°C for 5 min, then held at 4°C (Alison East, pers. comm.). An
amplified product of 1.1 kb was detected from the culture isolate of sevu.
The outbreak described in this report draws attention to the emergence of
new foodborne pathogens and to their association with unusual foods. Human
botulism is commonly caused by C. botulinum neurotoxin type A, B, and E
(4). In the present study, we showed that a neurotoxigenic C. butyricum was
present in the food implicated in a clinically suspected outbreak of
botulism in Gujrat, India.
Laboratory studies could not confirm the diagnosis of botulism because
clinical materials (such as contents of the gastrointestinal tract, feces)
were not submitted for examination for the presence of the botulinum toxin
or organisms. It is not surprising that toxin could not be detected in the
eight serum samples received by our laboratory. Because of the delay in
clinical diagnosis, early serum samples could not be obtained. Toxin is
detected in only 13% of serum samples collected more than 2 days after
ingestion of botulinum toxin (5). However, the clinical presentation of the
patients, response to trivalent botulinum antitoxin, and isolation of
toxigenic C. butyricum from one of the consumed food articles strongly
suggest that the outbreak was caused by food contaminated with toxigenic C.
butyricum.
Neurotoxigenic C. butyricum was first reported in 1986 in two cases of
infant botulism in Rome (6). Recently, neurotoxigenic C. butyricum was
isolated from the food implicated in an outbreak of clinically diagnosed
type E botulism in China (7). In this outbreak, it appears that sevu,
because of improper storage, was contaminated with the spores of C.
butyricum, which subsequently germinated and produced toxin. To the best of
our knowledge, this is the first report of neurotoxigenic C. butyricum
causing foodborne botulism in India.
The changing epidemiology of foodborne disease as highlighted in this
report calls for improved surveillance, including the development of new
technology for identifying outbreaks.
We thank Alison East, Institute of Food Research, Reading Laboratory,
United Kingdom, for supplying E. coli clones with BONT gene for PCR;
Pradeep Seth, professor and head, Department of Microbiology, All India
Institute of Medical Sciences for facilities provided; Biomed Warsaw,
Poland, for polyvalent botulinum antitoxin; and the medical and paramedical
staff of Civil Hospital, Ahemdabad.
Rama Chaudhry,* Benu Dhawan,* Dinesh Kumar,* Rajesh Bhatia,† J.C Gandhi,‡
R.K. Patel,§ and B.C. Purohit§
All India Institute of Medical Sciences, New Delhi, India; †National
Institute of Communicable Diseases, Delhi, India; ‡Health Medical Services
and Medical Education (H.S.), Gandhi Nagar, India; and §Civil Hospital,
Ahemdabad, Gujrat, India
References
1. Hatheway CL. Botulism. In: Balows A, Hausler WJ, Lennette EH, editors.
Laboratory diagnosis of infectious diseases: principles and practice.
New York: Springer-Verlag: 1988. p. 111-33.
2. McCroskey LM, Hatheway CL, Fenicia L, Pasolini B, Aureli P.
Characterization of an organism that produces type E botulinal toxin
but which resembles Clostridium butyricum from the feces of an infant
with type E botulism. J Clin Microbiol 1986;23:201-2.
3. Campbell KD, Collins MD, East AK. Gene probes for identification of
the Botulinal Neurotoxin gene and specific identification of
neurotoxin types B.E. and F.J. Clin Microbiol 1993;31:2255-62.
4. Hatheway CL. Clostridium botulinum and other clostridia that produce
botulinum neurotoxin. In: Hauschild AHW, Dodds KL, editors.
Clostridium botulinum—ecology and control in foods. New York: Marcel
Dekker, Inc.; 1992. p. 3-20.
5. Woodruff BA, Griffin PM, McCroskey LM, Smart JF, Wainwright RB, Bryant
RG, et al. Clinical and laboratory comparison of botulism from toxin
types A, B, and E in the United States, 1975-1988. J Infect Dis
1992;166:1281-6.
6. Aureli PK, Fenicia L, Pasolini B, Gianfranceschi M, McCroskey LM,
Hatheway CL. VII. Two cases of type E infant botulism caused by
neurotoxigenic Clostridium butyricum in Italy. J Infect Dis
1986;154:207-11.
7. Meng X, Karasawa T, Zou K, Kuang X, Wang X, Lu C. et al.
Characterization of a neurotoxigenic Clostridium butyricum strain
isolated from the food implicated in an outbreak of food-borne type E
botulism. J Clin Microbiol 1997;35:2160-2.
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Molecular Analysis of Salmonella paratyphi A From an Outbreak in New Delhi,
India
To the Editor: In the context of emerging infectious diseases, enteric
fever caused by Salmonella paratyphi A deserves increased attention and
vigilance, although its severity is often milder than that of S. typhi
disease. Outbreaks associated with this organism are exceedingly rare but
have recently been reported in India (1) and Thailand. In India, the first
reported outbreak of disease associated with S. paratyphi A (1) provided an
opportunity to study the molecular epidemiology of infection caused by this
organism.
A total of 18 human blood isolates of S. paratyphi A, 13 from the outbreak
in New Delhi, India (from September to October 1996) (1) and 5 sporadic
isolates from cases unrelated to the outbreak, were used in this study. A
total of 36 culture-positive cases were detected during the 6-week
outbreak. All strains were phage type 1 and were sensitive to all
antibiotics tested. Isolates were analyzed by ribotyping and pulsed-field
gel electrophoresis (PFGE) (2,3). PFGE/ribotype profiles were assigned
arbitrary designations and analyzed by defining a similarity (Dice)
coefficient, F (3), where F = 1.0 indicates complete pattern identity and F
= 0, complete dissimilarity.
The five sporadic isolates of S. paratyphi A gave PFGE patterns following
XbaI (5'-TCTAGA-3') digestion that were unique and distinctly different,
with differences of 8 to 12 bands (F = 0.63-0.70). In contrast, the 13
outbreak isolates shared only four closely related PFGE patterns differing
only in 1 to 6 bands (F = 0.8-1.0). Among the outbreak strains, two
distinct clones were observed, X1 and X2, which differed by 5 to 6 bands.
Furthermore, outbreak isolates X3 and X4 were closely related to X1,
differing by four and three DNA fragments, respectively. Similar results
were obtained after digestion with a second restriction endonuclease, SpeI
(5'-ACTAGT-3'; pattern designation S). Although fewer bands were seen
compared to PFGE, ribotyping of these isolates using SpeI-digested genomic
DNA largely confirmed the PFGE results in that the sporadic isolates gave
unique profiles and only three closely related ribotype profiles were
detected among the outbreak isolates. Two Malaysian isolates of S.
paratyphi A included for comparison gave patterns very different from the
Indian isolates by both PFGE (F = 0.44-0.65) and ribotyping. Also, it was
determined that isolates A-117 (X1/S1) and A-123 (X2/S2) belonged to the
index cases and that, as the outbreak progressed, other patterns (X3/S3 and
X4/S4), which differed from the original patterns by one to four bands,
appeared during weeks 2 to 3 of the outbreak. Notably, patterns X1 and X2
reappeared at the end of the outbreak.
Although molecular analysis of S. typhi and S. paratyphi B by ribotyping
(2,4) and PFGE (3) has been reported, to the best of our knowledge the
present study is the first performed with S. paratyphi A. The data obtained
agree with those observed for S. typhi (3) in that outbreak isolates are
more clonal and limited in diversity, whereas sporadic isolates are more
diverse genetically and belong to unrelated clones. According to the
criteria of Tenover et al. (5), it seems likely that the present outbreak
was associated with two distinct clones/strains of S. paratyphi A (X1/S1
and X2/S2) that are related (5) but have distinct PFGE profiles. This
observation is perhaps not surprising given the fact that both clones are
phage type 1 and that contaminated potable water was incriminated in the
outbreak (1). The PFGE results were largely confirmed by ribotyping,
although this technique appears to be slightly less sensitive and
discriminating in that fewer bands were seen and the differences between
outbreak isolates were much less obvious.
We thus conclude that the outbreak in New Delhi, India, was caused by two
related but distinct clones of S. paratyphi A. There also appears to be
substantial genetic diversity among S. paratyphi A strains as the Malaysian
isolates were very different from those from India. The data also suggested
minor genetic changes among the S. paratyphi A isolates during the 2-month
outbreak. This observation agrees with the high mutation rates noted among
pathogenic Salmonella spp. (6) and the plasticity of the genome of
salmonellae associated with enteric fever (7). How these changes affected
the biologic behavior of these isolates will be the subject of further
study. Our study reaffirms the usefulness of PFGE and ribotyping in the
molecular typing and discrimination of individual Salmonella isolates for
epidemiologic investigations.
Kwai-Lin Thong,* Satheesh Nair,* Rama Chaudhry,† Pradeep Seth,† Arti
Kapil,† Dinesh Kumar,† Hema Kapoor,‡ Savithri Puthucheary,* and Tikki Pang*
*University of Malaya, Kuala Lumpur, Malaysia; †All India Institute of
Medical Sciences, New Delhi, India; and ‡Safdarjang Hospital, New Delhi,
India
References
1. Kapil A, Sood S, Reddaiah VP, Das B, Seth P. Paratyphoid fever due to
Salmonella enterica serotype paratyphi A. Emerg Infect Dis 1997;3:407.
2. Pang T, Altwegg M, Martinetti G, Koh CL, Puthucheary SD. Genetic
variation among Malaysian isolates of Salmonella typhi as detected by
ribosomal RNA gene restriction patterns. Microbiol Immunol
1992;36:539-43.
3. Thong KL, Cheong YM, Puthucheary S, Koh CL, Pang T. Epidemiologic
analysis of sporadic and outbreak Salmonella typhi isolates by pulsed
field gel electrophoresis. J Clin Microbiol 1994;32:1135-41.
4. Ezquerra E, Burnens A, Jones C, Stanley J. Genotypic typing and
phylogenetic analysis of Salmonella paratyphi B and S. java with
IS200. J Gen Microbiol 1993;139:2409-14.
5. Tenover FC, Arbeit RD, Goering RV, Mickelson PA, Murray BE, Persing
DH, et al. Interpreting chromosomal DNA restriction patterns produced
by pulsed field gel electrophoresis: criteria for bacterial strain
typing. J Clin Microbiol 1995;33:2233-9.
6. Leclerc JE, Li B, Payne WL, Cebula TA. High mutation frequencies among
Escherichia coli and Salmonella pathogens. Science 1996;274:1208-11.
7. Liu SL, Sanderson KE. Highly plastic chromosomal organization in
Salmonella typhi. Proc Natl Acad Sci U S A 1996;93;10303-8.
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Unrecognized Ebola Hemorrhagic Fever at Mosango Hospital during the 1995
Epidemic in Kikwit, Democratic Republic of the Congo
To the Editor: We report here the clinical description of a hemorrhagic
syndrome observed in Mosango General Hospital that, retrospectively, was
one of the first cases of the Ebola hemorrhagic fever outbreak in the
Bandundu province of former Zaire in the spring of 1995 (1).
Case
On April 20, 1995, a 70-year-old nun, working as a nurse in Kikwit General
Hospital, was admitted to Mosango General Hospital with a 5-day history of
fever, despite antimalarial treatment. The day before hospitalization she
had profuse diarrhea, vomiting, high fever, and severe agitation with
delirium. On arrival, quiet and apyretic, she complained of headache, loss
of appetite, and severe asthenia, but she walked to her room without help.
On examination, the only abnormalities recorded were severe dehydration and
oral thrush-like lesions, raising a suspicion of candidiasis. Pulse rate
was 80/min and blood pressure 120/80. Medical history included an amebiasis
liver abscess 15 years ago and chronic coronaritis since 1990.
Electrocardiogram (ECG) abnormalities were consistent with chronic diffuse
ischemia. Laboratory investigations showed the following values: few
trophozoites on a thick film; erythrocyte sedimentation rate (ESR) 15 mm/h;
bleeding time (BT) 7½ min; coagulation time (CT) 9 min; and white blood
cells (WBC) 8.4x10(sup 9)/L (73% neutrophils, 23% lymphocytes, 2% eosinophils, 1%
basophils, 1% mastocytes). Urinalysis showed proteinuria (++), hyaline
cylinders (+++), 50 white cells per field, and hematuria (+). The patient
was perfused with 4L/day of glucose and 1.5 g of quinine. She was kept in a
private room in the nearby nuns' convent.
Later during the day, high fever (40°C) and severe diarrhea with melena
developed; the pulse rate was normal (80/min). Typhoid fever was suspected
despite the lack of hepatosplenomegaly; Widal test was not available for
confirmation. Treatment was started with intravenous (i.v.) amoxicillin
(1g/6h during the first 24 h and then 1g/4h) and i.v. chloramphenicol
(2g/24h). Subsequently, coagulation abnormalities developed in addition to
the melena; vitamin K and epsilon amino caproic acid were added to i.v.
therapy. Watery vomits remained frequent and abundant, and the patient's
condition was unresponsive to treatment.
On hospitalization day 2, the clinical picture remained the same, with
severe asthenia, anorexia, abundant blackish diarrhea, and watery vomits.
An intractable hiccup developed. The fever remained in plateau around 40°C
with spikes. Obnubilation occurred during episodes of high fever. Pulse and
blood pressure remained stable. ECG showed no modifications. Cutaneous
examination detected for the first time a maculopapular rash and petechiae
on flanks and limbs, and the patient complained of gastric pain for which
the neurologic examination was normal. Urine was abundant and clear.
On hospitalization day 3, high fever continued, with some defervescence
during which the patient regained lucidity, although she responded only
with monosyllables because of the extreme asthenia and somnolence; diarrhea
persisted but without hemorrhage. The patient had less vomiting. Laboratory
data showed ESR 35 mm/h; BT 10 min; CT 12 min; WBC 12.6x10(sup 9)/L (70%
neutrophils, 24% lymphocytes, 2% eosinophils, 1% basophils, 3% mastocytes).
During the night, the patient maintained a high temperature, still with
temperature-pulse disparity. The diagnosis of typhoid fever was questioned,
and other diagnostic possibilities were reconsidered (shigellosis,
mononucleosis); leukocytosis was considered against the possibility of
Ebola hemorrhagic fever. Chloramphenicol was switched to rifampicin (1,200
mg/24h).
On April 23, the patient's status was unchanged with fever, asthenia, and
diarrhea. Later in the day, her condition deteriorated: petechiae could be
seen on the entire body, and for the first time, bruises and bleeding at
injection sites were observed and precluded intramuscular injections. The
patient had bleeding cracks on the lips and diffuse bleeding in the oral
cavity (i.e., gums, tongue). The volume of urine was low, and antibiotic
therapy was changed to cephalosporin.
On hospitalization day 5, hemorrhages increased, and fever remained high
until the end of the day, when it started to normalize. Urine volume was
still low (verified by vesical catheter) despite the i.v. rehydration of 4
L/day. Fresh blood transfusion (300 ml) did not slow the hemorrhaging;
disseminated intravascular coagulation was suspected, and heparin treatment
was started. The patient became comatose. The laboratory results showed ESR
55mm/h and WBC 30.2x10(sup 9)/L with an unchanged formula. No coagulation was
observed on BT and CT. Blood pressure fell (80/50); the clinical status
remained unchanged until the patient's death on April 25 at 10:00 a.m.
No special nursing precautions were taken either during the hospitalization
or after the death, and the body was transferred to Kikwit to be buried. On
April 30, another nun who took care of the index patient during the night
of April 23 became ill with fever, headache, and myalgia. Over the next few
days, the second patient had a clinical picture identical to that of the
index patient, including high fever, severe asthenia, vomiting, hiccups,
and diarrhea. On May 5, epistaxis and coagulation abnormalities developed,
followed by other clinical signs of the hemorrhagic syndrome. The second
patient was transferred to Kikwit General Hospital, where she died 6 days
later. A laboratory confirmation of Ebola hemorrhagic fever was made on a
blood specimen collected on May 5 and sent to Special Pathogens Branch
(Centers for Disease Control and Prevention, Atlanta, GA).
These cases of unrecognized Ebola hemorrhagic fever were part of the
hospital outbreak that precipitated and mobilized international community
efforts (2). Retrospectively, the clinical symptoms observed were typical
of Ebola hemorrhagic fever (3,4) and were described again in subsequent
patients during this outbreak (5). In tropical Africa, the presence of
hemorrhagic symptoms in the course of a febrile illness should raise the
possibility of one of the viral hemorrhagic fever diseases. In viral
hemorrhagic fevers, maculopapular rash is constantly observed only in
filovirus disease. Typically, the clinical laboratory findings include an
early lymphopenia and marked thrombocytopenia. Containment and barrier
nursing procedures should be initiated until the diagnosis of viral
hemorrhagic fever can be ruled out. The index patient described here was
the third patient transferred from Kikwit General Hospital in less than 1
month to die of a hemorrhagic illness after a few days of an unexplained
febrile syndrome. Two patients were health-care workers in Kikwit General
Hospital. This cluster of hemorrhagic illness and possible human-to-human
transmission, particularly among hospital staff, was (and should always be)
sufficient to suspect a viral hemorrhagic fever. The laboratory
confirmation of this presumptive diagnosis was the clenching factor in the
multinational effort in Kikwit.
Marie-Jo Bonnet, Philippe Akamituna, and Anicet Mazaya
Mosango General Hospital, Kikwit, République Démocratique du Congo
References
1. Muyembe T, Kipasa M, the International Scientific and Technical
Committee, WHO Collaborating Centre for Haemorrhagic Fevers. Ebola
haemorrhagic fever in Kikwit, Zaire. Lancet 1995;345:1448.
2. Khan AS, Kweteminga TF, Heymann DL, LeGuenno B, Nabeth P, Kerstiens B,
et al. The reemergence of Ebola hemorrhagic fever, Zaire, 1995. J
Infect Dis. In press 1998.
3. Piot P, Sureau P, Breman JG, Heymann D, Kintoki V, Masamba M, et al.
Clinical aspects of Ebola virus infection in Yambuku area, Zaire,
1976. In: Pattyn SR, editor. Ebola virus haemorrhagic fever.
Amsterdam: Elsevier/North-Holland Biomedical Press; 1977. p. 7-14.
4. Sureau PH. Firsthand clinical observations of hemorrhagic
manifestations in Ebola hemorrhagic fever in Kitwit, Democratic
Republic of the Congo (former Zaire): clinical observations in 103
patients. Review of Infectious Diseases 1989;11:S790-3.
5. Bwaka MA, Bonnet M-J, Calain P, Colebunders R, De Roo A, Guimard Y, et
al. Ebola hemorrhagic fever in Kikwit, Democratic Republic of the
Congo (former Zaire): clinical observations in 103 patients. J Infect
Dis. In press 1998.
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Classification of Reactive Arthritides
To the Editor: We read with interest J.A. Lindsay's article on sequelae of
foodborne disease (1). However, we believe that there are errors in the
classification of the reactive arthritides. Lindsay states that ankylosing
spondylitis (AS) is a "rheumatoid inflammation of synovial joints and
entheses within and distal to the spine." Although not the primary focus of
the article, the classification and etiopathogeneses of rheumatoid
arthritis (RA) and the seronegative spondyloarthropathies, including AS,
should be clarified. The term spondylitis, from the Greek spondylos, for
vertebra, means inflammation of the vertebrae. The term rheumatoid is
generally taken to apply to rheumatoid arthritis, while rheumatic is a more
general term applying to all connective tissue diseases.
AS is a chronic, systemic, inflammatory disorder primarily affecting the
axial skeleton, with sacroiliac joint involvement as its hallmark. Back
pain is the first clinical manifestation in approximately 75% of the
patients (2). The backache is usually insidious in onset, dull, and
difficult to localize. After several months, it generally becomes bilateral
and persistent. The ache is often worse in the morning or after periods of
inactivity and improves with movement. The course is highly variable.
Involvement of peripheral joints other than hips and shoulders is uncommon.
AS is strongly associated with human leukocyte antigen (HLA) B27, a major
histocompatibility complex (MHC) class I allele, and may show familial
aggregation. More than 90% of patients with AS have the HLA-B27 allele (3).
HLA-B27 is believed to be directly involved in disease pathogenesis.
Transgenic rats expressing human HLA-B27 develop a broad spectrum of
disease closely resembling human disease. These rats have peripheral and
axial arthritis, gastrointestinal inflammation, and diarrhea.
Psoriatic-like skin changes and inflammation of the heart and male
genitalia are also seen. Histologically, the joint, gut, skin, and heart
lesions resemble those seen in HLA-B27-related disease in humans (4).
The inflammatory process in AS involves the synovial and cartilaginous
joints, as well as the osseous attachments of tendons and ligaments
(entheses). Much of the skeletal pathology of AS can be explained by the
changes that take place at the entheses. After an initial inflammatory,
erosive process involving the entheses, there is healing in which new bone
is formed. The final outcome of this process is an irregular bony
prominence with sclerosis of the adjacent cancellous bone (5). This can be
contrasted with the pathology of RA, in which there is a greater tendency
to affect cartilaginous joints such as the intervertebral discs and
symphysis pubis. The process in RA is one of bony erosion rather than new
bone formation.
The term ankylosing spondylitis, derived from the Greek for "bent spinal
vertebrae," by definition requires exclusion of the other
spondyloarthropathies, such as Reiter syndrome and reactive arthritides due
to enteric (or urogenital) organisms. Spondylitis may occur in reactive
arthritis, psoriatic arthritis, or the arthropathy associated with
inflammatory bowel disease, but is less common in these diseases
(approximately 50% in reactive arthritis, 20% in enteric arthritis or
psoriatic arthritis). All of these diseases can be viewed as seronegative
spondyloarthropathies in that, by definition, rheumatoid factor is not
present.
RA is a systemic autoimmune disorder of unknown etiology. It is a chronic
symmetric arthropathy of peripheral joints, associated with erosive
synovitis. Enthesopathy is generally not found. The majority of patients
have elevated titers of serum rheumatoid factor, as opposed to the
seronegative spondyloarthropathies. Spinal involvement in RA is seen but
most often involves the cervical spine. The pathogenesis of the spinal
disease is that of synovitis of the odontoid-atlas joints. The major HLA
association is with HLA-DR4, an MHC class II allele.
Reactive arthritis is so named because it is felt that the arthritis and
other inflammatory manifestations are an immune reaction to a distant
infection. There is an association with HLA-B27 but less so than that found
in AS (60% to 80%, compared with more than 90% in AS). While bacterial
antigens can be found within the joint, the offending infectious process
most often subsides before the onset of arthritis, and no living organisms
are found in the joint (2). In many cases, no infectious trigger can be
identified. Persistence of microbial antigens has been demonstrated and is
likely to play a prominent role in the pathogenesis of acute and chronic
inflammation. Antigens to several gastrointestinal pathogens have been
isolated from the synovial fluid in patients with reactive arthritis.
Salmonella, Shigella, Yersinia, Campylobacter, and Borrelia are the most
common pathogens capable of initiating reactive arthritis (2). The
arthritis is generally an asymmetric oligoarthritis predominantly affecting
the lower extremities and typically develops 6 to 14 days after a bout of
diarrhea. However, onset can occur up to 3 months later. Diarrhea can also
be absent, and there is no relationship between the severity of the
arthritis and the severity of the diarrhea.
Reiter syndrome is in fact a reactive arthritis. In 1916, Hans Reiter
described a triad of arthritis, urethritis, and conjunctivitis in a soldier
with dysentery. However, the disease was actually first described by Sir
Benjamin Brodie in the early 1800s (6). The complete triad is actually seen
in only a minority of patients. Arthritis develops 1 to 3 weeks after the
diarrhea or urethritis. It is generally asymmetric, involving large joints,
especially in the lower extremities. The term Reiter syndrome actually
refers only to the triad of arthritis, urethritis, and conjunctivitis.
Reiter syndrome is both clinically and historically more accurately termed
reactive arthritis. Nevertheless, the term reactive arthritis does not
reflect the systemic nature of the disease.
In summary, while both reactive arthritis and ankylosing spondylitis are
seronegative spondyloarthropathies, they are separate entities. Both are
distinct from rheumatoid arthritis.
Darren R. Blumberg and Victor S. Sloan
Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA
References
1. Lindsay JA. Chronic sequelae of foodborne disease. Emerg Infect Dis
1997;3:443-52.
2. Veys EM, Mielants H. Enteropathic arthropathies. In: Klippel JH,
Dieppe PA, editors. Rheumatology. St. Louis: 1994; 3.35.
3. Khan MA. Seronegative spondyloarthropathies. In: Schumache HR, editor.
Primer on rheumatic diseases. Atlanta (GA): Arthritis Foundation;
1993.
4. Hammer RE, Maika SD, Richardson JA, Tang J-P, Taurog JD. Spontaneous
inflammatory disease in transgenic rats expressing HLA-B27 and human
a2m: an animal model of HLA-B27-associated human disorders. Cell
1990;63:1099-112.
5. El-Khoury GY, Kathol MH, Brandser EA. Seronegative
spondyloarthropathies. Radiol Clin North Am 1996;34:343-57.
6. Toivanen A. Reactive arthritis. In: Klippel JH, Dieppe PA, editors.
Rheumatology. St. Louis: 1994: 4.9.
---------------------------------------------------------------------------
Reply to Drs. Blumberg and Sloan
To the Editor: I concur with your comments. After reviewing the literature
related to foodborne disease, it appears that the original classification
of reactive arthritides has been in error for some time. I certainly
appreciate the correction.
James A. Lindsay
University of Florida, Gainesville, Florida, USA
---------------------------------------------------------------------------
Cost of Blood Screening
To the Editor: In reference to G.A. Schmunis' article on the risk for
transfusion-transmitted infections in Central and South America (1), I
would like to comment on the cost of blood screening. In a screening
program, the objective is to have safe blood units, not to assess the
prevalence of different infections among potential or actual donors. Thus,
while acknowledging all infections present in a given donor or potential
donor is not required, detecting at least one of the infections that would
make a donor noneligible is. If samples from every potential donor are
subjected (by default) to all the tests, information on every infection
present is provided, and the cost of screening this donor is the sum of the
cost of every test applied; in this case, both the information and the cost
are greater than necessary.
Information on the prevalence of bloodborne infections among the general
population or, preferably, among potential donors (particularly where
professional donors are frequent) along with information on the costs of
the tests to be used can form the basis of a stepwise screening scheme.
Tests for infections with the highest prevalence would be applied first.
For example, in many areas of Peru, using the Venereal Disease Research
Laboratory (VDRL) test (for screening Treponema pallidum infection) first
would reduce the number of samples to be subjected to other more expensive
and often less available tests (e.g., HIV enzyme-linked immunosorbent assay
[ELISA] or hepatitis C virus [HCV] ELISA); in others areas, a test for
hepatitis B virus antigen (HB(sub s)Ag) should be used before HIV ELISA. The
reduction in cost provided by stepwise screening will depend on the
prevalences of the more frequent infections and the frequency of concurrent
infections.
The questionnaires applied to candidate donors should be validated, and the
benefit of using them should be assessed. In most settings, candidate
donors are either ignorant of their status as carriers of bloodborne
infection or ready to deny it; therefore, the questionnaire is of little
use. In some cases candidate donors are turned down because of "hepatitis
history" when in fact they have not had bloodborne hepatitis.
Finally, screening tests seem to be quite more expensive than reported in
Table 4 of the Schmunis article. In Lima, at a ministry of health facility,
some prices are as follows: HIV ELISA US$12.50, VDRL US$6.40, HBsAg
US$13.90.
O. Jaime Chang
Instituto Nacional de Salud, Ministerio de Salud, Lima, Peru
Reference
1. Schmunis GA, Zicker F, Pinheiro F, Brandling-Bennett D. Risk for
transfusion-transmitted infectious diseases in Central and South
America. Emerg Infect Dis 1998;1:5-11.
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Book Review
Emerging Infections
R.M. Krause, Editor. Academic Press, New York, 1998, 513 pages.
---------------------------------------------------------------------------
Emerging Infections is the first volume in a new series entitled Biomedical
Research Reports, edited by John Gallin and Anthony Fauci. The volume
contains 17 chapters, all outstanding and for the most part both timely and
comprehensive, written by experts in the field. After an intellectually
stimulating introductory chapter by Richard Krause, we are treated to an
analysis of epidemics by one of the supreme authorities, Roy Anderson of
Oxford University. Included here is a valuable discussion on the
transmission of microbial infections in populations as well as the
development of drug resistance.
Chapters on emerging bacterial diseases include a superb one on Persisting
Problems in Tuberculosis, by McKinney, Jacobs, and Bloom, which is right up
to date yet includes fascinating literary quotes, from Charles Dickens to
Sir Arthur Conan Doyle. The possible role of mobile genetic elements in the
emergence of new strains of cholera is briefly discussed by Rubin, Waldor,
and Mekalanos. Escherichia coli O157:H7 and its evolution as an emerging
infectious disease are considered by Whittam, McGraw, and Reid. A useful
overview of group A streptococcal diseases, combined with an overview of
staphylococcal toxic shock syndrome, is given by Musser and Krause and
followed by a scholarly account of Lyme disease by Allen Steere. Finally,
Davies and Webb devote nearly 40 pages to a discussion of the emergence of
antibiotic resistance in bacteria.
There are six chapters on viral diseases, beginning with Robert Webster on
influenza, the classic pandemic disease threat. Webster's review provides a
remarkably current description (up to mid-1997) of what we know about
influenza pandemics and their origins, including a discussion of the first
H5N1 influenza case in a human in Hong Kong. The emergence of dengue and
the complexities of dengue hemorrhagic fever and dengue shock syndrome are
reviewed by Holmes, Bartley, and Garnett of Oxford University, with a
strong emphasis on the epidemiologic aspects. This discussion is followed
by an authoritative review of the AIDS epidemic by Quinn and Fauci, who
include sobering predictions of future epidemics in Asia and Africa.
A short chapter on hantavirus by Nathanson and Nichol is followed by a
searching account of Ebola virus emergences, including fascinating
speculations on their possible origin, by Murphy and Peters. The final
chapter, related to virus diseases, by Tabachnick, considers
arthropod-borne pathogens and is dedicated to George Craig, a leader in the
field of vector biology.
Two chapters are devoted to emerging parasitic diseases. Adel Mahmoud
reviews Giardia, Cryptosporidium, Isospora, and Cyclospora organisms, whose
role in human diseases has only recently been recognized. Karen Day of
Oxford University discusses malarial infection and disease and the factors
that have led to the current world in which the effects of malaria in many
regions are the same or worse than at the turn of the century.
Finally, a chapter on transmissible spongiform encephalopathies by Hope
brings us up to 1996 when new variant Creutzfeldt-Jakob disease (bovine
spongiform encephalopathy agent in humans) was first recognized.
Emerging Infections sets a high standard for future volumes in this series.
Nicely produced, it is recommended reading for everyone with an interest in
infectious diseases and in strategies for research, understanding, and
control of the complex factors that lead to infectious disease emergence
and reemergence.
Brian W. J. Mahy
Centers for Disease Control and Prevention, Atlanta, Georgia, USA
-------------------------------------------------------------------------------
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News and Notes
CDC To Release Updated Emerging Infectious Disease Plan
Preventing Emerging Infectious Diseases: A Strategy for the 21st Century
outlines new measures toward achieving emerging infectious disease
prevention and control. The updated plan signals the second phase of the
campaign launched in 1994 with the publication of Addressing Emerging
Infectious Disease Threats: A Prevention Strategy for the United States, a
collaborative effort of the Centers for Disease Control and Prevention
under the leadership of the National Center for Infectious Diseases and
institutions and agencies throughout the United States and abroad.
The objectives and activities in the updated plan are organized under the
same four goals described in the 1994 publication: surveillance and
response, applied research, infrastructure and training, and prevention and
control. Nine specific priority program areas are outlined: antimicrobial
resistance; foodborne and waterborne diseases; vector-borne and zoonotic
diseases; diseases transmitted through blood transfusions or blood
products; chronic diseases caused by infectious agents; vaccine development
and use; diseases of people with impaired host defenses; diseases of
pregnant women and newborns; and diseases of travelers, immigrants, and
refugees.
Achieving the goals outlined in the updated plan will continue to require
sustained and coordinated efforts of agencies and organizations, state and
local health departments (surveillance of infectious diseases), academic
centers and other federal agencies (research), health-care providers and
health-care networks (guideline development and dissemination),
international organizations (outbreak responses overseas), and other
partners.
The executive summary of Preventing Emerging Infectious Diseases: A
Strategy for the 21st Century will be released as a special issue of the
Morbidity and Mortality Weekly Report on September 10, 1998. An electronic
version of the full document as well as information on how to order a print
copy will be available shortly afterwards at
http://www.cdc.gov/ncidod/ncid.htm.
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First Congress of the European Society for Emerging Infections, September
13-16, 1998, Budapest, Hungary
Founded in 1997 by human and veterinary infectious disease specialists, the
European Society for Emerging Infections (ESEI) forms a European network
for the study of new or emerging infectious diseases. This
interdisciplinary forum was a necessity because most emerging infections
are zoonoses or are linked with animal care or with animal product
handling. ESEI is holding its first International Congress in the Atrium
Hyatt Conference Centre, Budapest, Hungary, September 13-16, 1998. The
opening lecture, "Emerging infections—an overview," will be given by Prof.
Luc Montagnier. The meeting will consist of invited lectures, two free
paper sessions, a roundtable discussion, and daily poster presentations.
Conference topics include risk factors for emergence of pathogens,
tick-borne diseases, hantavirus infections, transmissible spongiform
encephalopathies, Borna disease, lyssavirus infections, and foodborne
diseases. A banquet cruise on the Danube will end the Congress on Wednesday
evening, September 16, 1998.
Abstracts should address one of the above topics and be submitted before
the deadline of May 31, 1998. For more information, please contact ESEI
President Prof. M. Granström, Microbiology, Karolinska Hospital, S-171 76
Stockholm, Sweden; fax: 46-8-30-80-99; e-mail: marta@mb.ks.se or the local
organizer Dr. A. Lakos, Centre for Tick-borne Diseases, Visegradi 14,
H-1132 Budapest, Hungary, fax: 36-1-349-49-26, e-mail: alakos@helka.iif.hu.
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Foodborne Illness: A Disease for All Seasons, October 27 and 28, 1998,
Newark, Delaware
Sponsored by the Public Health Laboratories of Delaware, Maryland, New
Jersey, and Pennsylvania and the National Laboratory Training Network,
Eastern Office, this seminar will provide up-to-date information on changes
in epidemiology in foodborne diseases, emerging infectious organisms,
proper food and clinical specimen collection and testing, and strategies to
decrease foodborne illness. Speakers will represent the Centers for Disease
Control and Prevention, the Food and Drug Administration, Minnesota
Department of Agriculture, Minnesota Department of Public Health, and the
University of Maryland.
For more information, contact Christine Ford, National Laboratory Training
Network, Eastern Office, Delaware Public Health Laboratory; tel.:
302-653-2841; fax: 302-653-2844; e-mail: ford115w@cdc.gov.
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December 1998 International Conference on Antiretroviral Therapy, St.
Thomas, West Indies
The International Medical Press will sponsor the International Conference
on the Discovery and Clinical Development of Antiretroviral Therapies from
December 13-17, 1998. In addition to plenary talks from invited speakers,
the conference will feature oral presentations based on selected abstracts
and scientific poster sessions. Topics include drug design and discovery,
chemistry and preclinical development, pharmacology, virology and drug
resistance, and clinical development (phase I/II/III and novel combination
therapies).
Registration is limited, and preference will be given to those delegates
who submit an abstract. For further information, contact the International
Medical Press; tel: 404-233-6446; fax 404-233-2827; e-mail:
ICDCD@intmedpress.com; or Website: http://www.intmedpress.com/ICDCD.
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Erratum
Vol. 4, No. 2
In the article, "Accommodating Error Analysis in Comparison and Clustering
of Molecular Fingerprints, by H. Salamon, M.R. Segal, A. Ponce de Leon, and
P.M. Small, in Table 1 on page 162, mean kilobases for H37Rv band 12 should
be 0.936.
Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA
URL: ftp://ftp.cdc.gov/pub/EID/vol4no3/ascii/vol4no3.txt
Please note that figures and equations are not available in ASCII format;
their placement within the text is noted by [fig] and [eq], respectively.
Greek symbols are spelled out. The following codes are used:
(ft) for footnote; (sup) for superscript; (sub) for subscript;
= for greater than or equal to.